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// bpf translation pass
// Copyright (C) 2016-2020 Red Hat Inc.
//
// This file is part of systemtap, and is free software. You can
// redistribute it and/or modify it under the terms of the GNU General
// Public License (GPL); either version 2, or (at your option) any
// later version.
#include "config.h"
#include "staptree.h"
#include "session.h"
#include <iostream>
#include <cassert>
#include "bpf-internal.h"
#include "bpf-bitset.h"
namespace bpf {
// Allocate space on the stack and store a string literal in that space:
static value *
alloc_literal_str(program &p, insn_inserter &ins, value *s)
{
std::string str = s->str();
size_t str_bytes = str.size() + 1;
str_bytes += 4 - str_bytes % 4; // write aligned words to avoid garbage data
int ofs; size_t tmp_space;
if (s->is_format() && str_bytes <= BPF_MAXSTRINGLEN * 2)
{
// PR23068 workaround mitigation to reduce stack pressure:
//
// Store format strings in the top of the stack, since at most
// one printf() operation is prepared at a time and other string
// values will not be stored in that area now.
ofs = -str_bytes;
goto write_string;
}
// Append the string to existing temporary data.
//
// TODO: This could produce significant space limitations.
// A better solution would be to integrate with the
// register allocator and reclaim the space after
// the string literal is no longer live.
tmp_space = p.max_tmp_space;
tmp_space += 4 - tmp_space % 4; // write aligned words to avoid verifier error
p.use_tmp_space(tmp_space);
if (tmp_space + str_bytes > MAX_BPF_STACK(p.target))
throw std::runtime_error("string allocation failed due to lack of room on stack");
tmp_space += str_bytes;
#if 1
// The following aren't ideal because an unlucky ordering of
// allocation requests will waste additional space.
// XXX PR23860: Passing a short (non-padded) string constant can fail
// the verifier, which is not smart enough to determine that accesses
// past the end of the string will never occur. To fix this, make sure
// the string offset is at least -BPF_MAXSTRINGLEN.
//if (!s->is_format() && tmp_space < BPF_MAXSTRINGLEN)
// tmp_space = BPF_MAXSTRINGLEN;
// TODO PR23860: An even uglier workaround for emit_string_copy()
// overlapping source and destination regions. Only do this for
// non-format strings, as format strings are not manipulated by the
// eBPF program.
if (!s->is_format() && tmp_space < BPF_MAXSTRINGLEN * 2 + str_bytes)
tmp_space = BPF_MAXSTRINGLEN * 2 + str_bytes;
#endif
p.use_tmp_space(tmp_space);
ofs = -tmp_space;
write_string:
value *frame = p.lookup_reg(BPF_REG_10);
value *out = emit_simple_literal_str(p, ins, frame, ofs, str, false /* don't zero pad */);
return out;
}
static void
lower_str_values(program &p)
{
const unsigned nblocks = p.blocks.size();
for (unsigned i = 0; i < nblocks; ++i)
{
block *b = p.blocks[i];
for (insn *j = b->first; j != NULL; j = j->next)
{
value *s0 = j->src0;
if (s0 && s0->is_str())
{
insn_before_inserter ins(b, j, "str");
std::string str0 = s0->str();
value *new_s0 = alloc_literal_str(p, ins, s0);
j->src0 = new_s0;
}
value *s1 = j->src1;
if (s1 && s1->is_str())
{
insn_before_inserter ins(b, j, "str");
std::string str1 = s1->str();
value *new_s1 = alloc_literal_str(p, ins, s1);
j->src1 = new_s1;
}
}
}
}
static void
fixup_operands(program &p)
{
const unsigned nblocks = p.blocks.size();
for (unsigned i = 0; i < nblocks; ++i)
{
block *b = p.blocks[i];
for (insn *j = b->first; j != NULL; j = j->next)
{
// Any plain move is already handled.
if (j->is_move())
continue;
// The second source cannot handle 64-bit integers.
value *s1 = j->src1;
if (s1 && s1->is_imm() && s1->imm() != (int32_t)s1->imm())
{
value *n = p.new_reg();
insn_before_inserter ins(b, j, "opt");
p.mk_mov(ins, n, s1);
j->src1 = s1 = n;
// Since the content is in the src register, we need
// to use BPF_STX instead of BPF_ST
j->code = BPF_STX | BPF_MEM | BPF_W;
}
if (value *s0 = j->src0)
{
if (value *d = j->dest)
{
// Binary operators must have dest == src0.
if (d == s0)
;
else if (d == s1)
{
if (j->is_commutative())
{
j->src0 = s1;
j->src1 = s0;
}
else
{
// Special care for x = y - x
value *n = p.new_reg();
{
insn_before_inserter ins(b, j, "opt");
p.mk_mov(ins, n, s0);
}
j->src0 = n;
j->dest = n;
{
insn_after_inserter ins(b, j, "opt");
p.mk_mov(ins, d, n);
}
}
}
else
{
// Transform { x = y - z } to { x = y; x -= z; }
insn_before_inserter ins(b, j, "opt");
p.mk_mov(ins, d, s0);
j->src0 = d;
}
}
else if (s0->is_imm())
{
// Comparisons can't have src0 constant.
value *n = p.new_reg();
insn_before_inserter ins(b, j, "opt");
p.mk_mov(ins, n, s0);
j->src0 = n;
}
}
}
}
}
static void
thread_jumps(program &p)
{
const unsigned nblocks = p.blocks.size ();
std::vector<block *> fwds(nblocks);
// Identify blocks that do nothing except jump to another block.
for (unsigned i = 0; i < nblocks; ++i)
fwds[i] = p.blocks[i]->is_forwarder ();
// Propagate chains of forwarder blocks.
{
bool changed;
do
{
changed = false;
for (unsigned i = 0; i < nblocks; ++i)
if (block *fi = fwds[i])
{
unsigned j = fi->id;
if (block *fj = fwds[j])
{
if (i != j)
{
fwds[i] = fj;
changed = true;
}
}
}
}
while (changed);
}
// Perform jump threading.
for (unsigned i = 0; i < nblocks; ++i)
{
block *b = p.blocks[i];
if (edge *e = b->taken)
{
if (block *n = fwds[e->next->id])
e->redirect_next (n);
}
if (edge *e = b->fallthru)
{
if (block *n = fwds[e->next->id])
e->redirect_next (n);
}
}
}
static void
fold_jumps(program &p)
{
const unsigned nblocks = p.blocks.size ();
for (unsigned i = 0; i < nblocks; ++i)
{
block *b = p.blocks[i];
if (b->taken
&& b->fallthru
&& b->taken->next == b->fallthru->next)
{
insn *l = b->last;
assert (BPF_CLASS (l->code) == BPF_JMP);
l->code = BPF_JMP | BPF_JA;
delete b->fallthru;
}
}
}
static void
reorder_blocks(program &p)
{
unsigned nblocks = p.blocks.size ();
std::vector<bool> visited(nblocks);
std::vector<block *> ordered;
std::vector<block *> worklist;
// Begin with the entry block.
worklist.push_back(p.blocks[0]);
// Iterate until all blocks placed.
while (!worklist.empty())
{
block *b = worklist.back ();
worklist.pop_back ();
// Don't place a block twice, we're not duplicating paths.
if (visited[b->id])
continue;
// Place this block now.
ordered.push_back (b);
visited[b->id] = true;
edge *t = b->taken;
edge *f = b->fallthru;
// Look for an IF-THEN triangle where the IF condition might
// do well to be reversed. We could find larger subgraphs with
// postdominators, but since we can't reverse all jumps, it's
// probably not worth it. Also look for cases where the taken
// edge has not been placed, but the fallthru has.
if (t && f
&& ((t->next->fallthru && t->next->fallthru->next == f->next)
|| (visited[f->next->id] && !visited[t->next->id])))
switch (b->last->code)
{
case BPF_JMP | BPF_JEQ | BPF_X:
case BPF_JMP | BPF_JEQ | BPF_K:
case BPF_JMP | BPF_JNE | BPF_X:
case BPF_JMP | BPF_JNE | BPF_K:
b->last->code ^= BPF_JEQ ^ BPF_JNE;
std::swap (t, f);
b->taken = t;
b->fallthru = f;
break;
}
// Plase the two subsequent blocks.
// Note the LIFO nature of the worklist and place fallthru second.
if (t)
{
block *o = t->next;
if (!visited[o->id])
worklist.push_back (o);
}
if (f)
{
block *o = f->next;
if (visited[o->id])
{
// The fallthru has been placed. This means that we
// require an extra jump, and possibly a new block in
// which to hold it.
if (t)
{
block *n = p.new_block ();
insn_append_inserter ins(n, "opt");
p.mk_jmp (ins, o);
ordered.push_back (n);
f->redirect_next (n);
}
else
{
delete f;
insn_after_inserter ins(b, b->last, "opt");
p.mk_jmp (ins, o);
}
}
else
worklist.push_back (o);
}
}
// Remove any unreachable blocks.
for (unsigned i = 0; i < nblocks; ++i)
if (!visited[i])
{
// XXX: Before any of the unreachable blocks are deleted,
// any edges between other blocks that lead to the current
// block are set as nullptr. This eliminates access to the
// deleted blocks.
for (edge *e: p.blocks[i]->prevs)
{
if (e == e->prev->fallthru)
e->prev->fallthru = nullptr;
else if (e == e->prev->taken)
e->prev->taken = nullptr;
}
delete p.blocks[i];
p.blocks[i] = nullptr;
}
// Renumber the blocks for the new ordering.
nblocks = ordered.size ();
for (unsigned i = 0; i < nblocks; ++i)
{
block *b = ordered[i];
b->id = i;
}
p.blocks = ordered;
}
struct interference_graph
{
// ??? Quadratic size for a sparsely populated set. However, for small
// sizes (less than hundreds of registers) this is probably more time
// and space efficient than std::set<std::pair<regno, regno>>.
bitset::set2 data;
interference_graph(size_t n) : data(n, n) { }
bool test(unsigned a, unsigned b) const
{
return data[a].test(b);
}
void add(unsigned a, unsigned b)
{
data[a].set(b);
data[b].set(a);
}
void merge(unsigned a, unsigned b)
{
data[a] |= data[b];
data[b] = data[a];
}
};
struct copy_graph
{
struct entry
{
unsigned short count;
regno i, j;
entry(regno ii, regno jj) : count(0), i(ii), j(jj) { }
bool operator< (const entry &o) const
{
return (count < o.count
|| (count == o.count
&& (i < o.i || (i == o.i && j < o.j))));
}
};
std::vector<entry> data;
std::unordered_map<uint32_t, uint32_t> map;
void add(regno i, regno j);
void sort();
};
void
copy_graph::add(regno i, regno j)
{
if (i == j)
return;
if (i > j)
std::swap(i, j);
uint32_t ij = (uint32_t)i << 16 | j;
uint32_t k;
auto iter = map.find(ij);
if (iter == map.end())
{
k = data.size();
data.push_back(entry(i, j));
auto ok = map.insert(std::pair<uint32_t, uint32_t>(ij, k));
assert(ok.second);
}
else
k = iter->second;
data[k].count += 1;
}
void
copy_graph::sort()
{
map.clear();
std::sort(data.begin(), data.end());
}
struct life_data
{
bitset::set2 live_in;
bitset::set2 live_out;
bitset::set2 used;
bitset::set2 killed;
bitset::set1 cross_call;
std::vector<unsigned short> uses;
unsigned short npartitions;
life_data(size_t nblocks, size_t nregs);
};
life_data::life_data(size_t nblocks, size_t nregs)
: live_in(nblocks, nregs),
live_out(nblocks, nregs),
used(nblocks, nregs),
killed(nblocks, nregs),
cross_call(nregs),
uses(nregs)
{ }
static void
find_lifetimes (life_data &d, program &p)
{
const unsigned nblocks = p.blocks.size();
const unsigned nregs = p.max_reg();
// Collect initial lifetime d from the blocks.
for (unsigned i = 0; i < nblocks; ++i)
{
block *b = p.blocks[i];
bitset::set1_ref killed = d.killed[i];
bitset::set1_ref used = d.used[i];
for (insn *j = b->last; j != NULL; j = j->prev)
{
// Every regno that is set in a block is part of killed.
j->mark_sets(killed, 1);
// Remove sets from used before adding the uses.
j->mark_sets(used, 0);
j->mark_uses(used, 1);
}
d.live_in[i] = used;
}
// Propagate lifetime d around blocks. We could reduce iteration
// by processing the blocks in post-dominator order. But the program
// sizes we must have (because of bpf restrictions) are is too small
// to worry about more than simple reverse order.
bool changed;
bitset::set1 tmp(nregs);
do
{
changed = false;
for (unsigned i = nblocks; i-- > 0; )
{
block *b = p.blocks[i];
if (b->taken)
{
tmp = d.live_in[b->taken->next->id];
if (b->fallthru)
tmp |= d.live_in[b->fallthru->next->id];
}
else if (b->fallthru)
tmp = d.live_in[b->fallthru->next->id];
else
tmp.clear();
d.live_out[i] = tmp;
tmp -= d.killed[i];
tmp |= d.used[i];
// Note that in order to ensure termination we must accumulate
// into live_in rather than assigning to it.
if (!tmp.is_subset_of (d.live_in[i]))
{
changed = true;
d.live_in[i] |= tmp;
}
}
}
while (changed);
}
static void
find_block_cgraph (copy_graph &cgraph, block *b)
{
for (insn *j = b->last; j != NULL; j = j->prev)
{
if (j->is_move() && j->src1->is_reg())
cgraph.add(j->dest->reg(), j->src1->reg());
else if (j->is_binary() && j->src0->is_reg())
cgraph.add(j->dest->reg(), j->src0->reg());
}
}
static void
find_cgraph (copy_graph &cgraph, const program &p)
{
const unsigned nblocks = p.blocks.size();
for (unsigned i = 0; i < nblocks; ++i)
find_block_cgraph (cgraph, p.blocks[i]);
}
static void
find_block_uses (std::vector<unsigned short> &uses, block *b)
{
for (insn *j = b->last; j != NULL; j = j->prev)
{
if (j->src0 && j->src0->is_reg())
++uses[j->src0->reg()];
if (j->src1 && j->src1->is_reg())
++uses[j->src1->reg()];
}
}
static void
find_uses (std::vector<unsigned short> &uses, const program &p)
{
const unsigned nblocks = p.blocks.size();
for (unsigned i = 0; i < nblocks; ++i)
find_block_uses (uses, p.blocks[i]);
}
static void
find_block_igraph (interference_graph &igraph, bitset::set1_ref &cross_call,
block *b, bitset::set1_ref &live)
{
for (insn *j = b->last; j != NULL; j = j->prev)
{
// Remove sets from used before adding the uses.
j->mark_sets(live, 0);
if (j->is_call())
cross_call |= live;
j->mark_uses(live, 1);
// We use another bitset to include the variables that are
// defined at this instruction in the interference.
bitset::set1 interference = live;
if (!j->is_call())
j->mark_sets(interference, 1);
// Record interference between two simultaneously live registers.
for (size_t r1 = interference.find_first();
r1 != bitset::set1_ref::npos;
r1 = interference.find_next (r1))
for (size_t r2 = interference.find_next(r1);
r2 != bitset::set1_ref::npos;
r2 = interference.find_next (r2))
igraph.add(r1, r2);
}
}
static void
find_igraph (interference_graph &igraph, life_data &d, program &p)
{
const unsigned nblocks = p.blocks.size();
const unsigned nregs = p.max_reg();
bitset::set1 tmp(nregs);
for (unsigned i = 0; i < nblocks; ++i)
{
tmp = d.live_out[i];
find_block_igraph (igraph, d.cross_call, p.blocks[i], tmp);
}
}
struct pref_sort_reg
{
const life_data &d;
pref_sort_reg(const life_data &dd) : d(dd) { }
bool cmp(regno a, regno b) const;
bool operator()(const regno &a, const regno &b) const { return cmp(a, b); }
};
bool
pref_sort_reg::cmp(regno a, regno b) const
{
// Prefer registers that cross calls first.
int diff = d.cross_call.test(a) - d.cross_call.test(b);
if (diff != 0)
return diff > 0;
// Prefer registers with more uses.
diff = d.uses[a] - d.uses[b];
if (diff != 0)
return diff > 0;
// Finally, make the sort stable by comparing regnos.
return a < b;
}
static void
merge_copies(std::vector<regno> &partition, life_data &life,
interference_graph &igraph, program &p)
{
copy_graph cgraph;
find_cgraph(cgraph, p);
cgraph.sort();
unsigned ncopies = cgraph.data.size();
for (unsigned i = 0; i < ncopies; ++i)
{
const copy_graph::entry &c = cgraph.data[i];
unsigned r1 = partition[c.i];
unsigned r2 = c.j;
if (r2 >= MAX_BPF_REG
&& partition[r2] == r2
&& !igraph.test(r1, r2)
&& (r1 >= BPF_REG_6 || !life.cross_call.test(r2)))
{
partition[r2] = r1;
igraph.merge(r1, r2);
life.cross_call[r1] |= life.cross_call[r2];
}
}
}
static void
merge(std::vector<regno> &partition, std::vector<regno> &ordered,
life_data &life, interference_graph &igraph, program &p)
{
unsigned nregs = p.max_reg();
for (unsigned i = MAX_BPF_REG; i < nregs; ++i)
{
unsigned r1 = ordered[i - MAX_BPF_REG];
if (partition[r1] != r1)
continue;
for (unsigned j = i + 1; j < nregs; ++j)
{
unsigned r2 = ordered[j - MAX_BPF_REG];
if (partition[r2] == r2)
{
bool interferes = false;
// check for interference between r1, r2 and any
// registers already merged with either r1 or r2.
for (unsigned k = MAX_BPF_REG; k < nregs; ++k)
{
unsigned r3 = ordered[k - MAX_BPF_REG];
if ((partition[r3] == r1 && igraph.test(r2, r3))
|| (partition[r3] == r2 && igraph.test(r1, r3)))
{
interferes = true;
break;
}
}
if (!interferes)
{
partition[r2] = r1;
igraph.merge(r1, r2);
life.cross_call[r1] |= life.cross_call[r2];
}
}
}
}
}
static unsigned
allocate(std::vector<regno> &partition, std::vector<regno> &ordered,
life_data &life, interference_graph &igraph, program &p)
{
// return 0 if allocation succeeds, otherwise return the first
// temporary that cannot be allocated.
unsigned nregs = p.max_reg();
for (unsigned i = MAX_BPF_REG; i < nregs; ++i)
{
unsigned r2 = ordered[i - MAX_BPF_REG];
// Propagate partition info from previous allocations.
if (partition[r2] != r2)
continue;
unsigned first;
if (life.cross_call.test(r2))
first = BPF_REG_6;
else
first = BPF_REG_0;
for (unsigned r1 = first; r1 < BPF_REG_10; ++r1)
{
bool interferes = false;
// check for interference between r1, r2 and any
// registers already merged with either r1 or r2.
for (unsigned k = MAX_BPF_REG; k < nregs; ++k)
{
unsigned r3 = ordered[k - MAX_BPF_REG];
if ((partition[r3] == r1 && igraph.test(r2, r3))
|| (partition[r3] == r2 && igraph.test(r1, r3)))
{
interferes = true;
break;
}
}
if (!interferes)
{
partition[r2] = r1;
igraph.merge(r1, r2);
goto done;
}
}
// We didn't find a color for r2.
return r2;
done:
;
}
return 0;
}
static unsigned
choose_spill_reg(unsigned tmpreg, std::vector<regno> &ordered, std::vector<bool> spilled)
{
unsigned ret = 0;
// Choose the lowest priority reg that has been allocated but not spilled.
// tmpreg is the first element in ordered that hasn't been allocated.
for (unsigned i = 0; i < ordered.size() && ordered[i] != tmpreg; ++i)
{
unsigned reg = ordered[i];
if (!spilled[reg])
ret = reg;
}
if (!ret)
throw std::runtime_error(_("unable to register allocate"));
spilled[ret] = true;
return ret;
}
static void
spill(unsigned reg, unsigned num_spills, program &p)
{
unsigned nblocks = p.blocks.size();
value *frame = p.lookup_reg(BPF_REG_10);
// Reserve reg's stack offset.
int off = BPF_REG_SIZE * (num_spills + 1) + p.max_tmp_space;
if (off > (int)p.max_reg_space)
p.max_reg_space = (unsigned)off;
// Ensure double word alignment.
if (off % BPF_REG_SIZE)
off += BPF_REG_SIZE - off % BPF_REG_SIZE;
if (off > MAX_BPF_STACK(p.target))
throw std::runtime_error(
_("register allocation failed due to insufficent BPF stack size"));
for (unsigned i = 0; i < nblocks; ++i)
{
block *b = p.blocks[i];
for (insn *j = b->last; j != NULL; j = j->prev)
{
value *src0 = j->src0;
value *src1 = j->src1;
value *dest = j->dest;
value *new_tmp = NULL;
// If reg is a source, insert a load before j
if ((src0 && src0->reg_val == reg) || (src1 && src1->reg_val == reg))
{
insn_before_inserter ins(b, j, "regalloc");
new_tmp = p.new_reg();
p.mk_ld (ins, BPF_DW, new_tmp, frame, -off);
// Replace reg with new_tmp
if (src0 && src0->reg_val == reg)
j->src0 = new_tmp;
if (src1 && src1->reg_val == reg)
j->src1 = new_tmp;
}
// If reg is the destination, insert a store after j
if (dest && dest->reg_val == reg)
{
insn_after_inserter ins(b, j, "regalloc");
new_tmp = new_tmp ?: p.new_reg();
p.mk_st (ins, BPF_DW, frame, -off, new_tmp);
j->dest = new_tmp;
}
}
}
return;
}
static void
finalize_allocation(std::vector<regno> &partition, program &p)
{
unsigned nregs = p.max_reg();
for (unsigned i = MAX_BPF_REG; i < nregs; ++i)
{
value *v = p.lookup_reg(i);
// Hard registers are partition[i] == i,
// and while other partition members should require
// no more than three dereferences to yield a hard reg,
// we allow for up to ten dereferences.
unsigned r = partition[i];
for (int j = 0; r >= MAX_BPF_REG && j < 10; j++)
r = partition[r];
assert(r < MAX_BPF_REG);
v->reg_val = r;
}
}
static void
reg_alloc(program &p)
{
bool done = false;
const unsigned nblocks = p.blocks.size();
std::vector<bool> spilled(p.max_reg());
for (unsigned num_spills = 0; !done; ++num_spills)
{
const unsigned nregs = p.max_reg();
life_data life(nblocks, nregs);
find_lifetimes(life, p);
find_uses(life.uses, p);
std::vector<regno> partition(nregs);
// Initially, all registers are in their own partition.
for (unsigned i = 0; i < nregs; ++i)
partition[i] = i;
// Compute the interference of all registers.
interference_graph igraph(nregs);
find_igraph (igraph, life, p);
// Merge non-conflicting partitions between copies first.
merge_copies(partition, life, igraph, p);
// Merge all other non-conflicting registers next.
std::vector<regno> ordered(nregs - MAX_BPF_REG);
for (unsigned i = MAX_BPF_REG; i < nregs; ++i)
ordered[i - MAX_BPF_REG] = i;
merge(partition, ordered, life, igraph, p);
// XXX: Consider using C++14 lambda.
pref_sort_reg sort_obj(life);
std::sort(ordered.begin(), ordered.end(), sort_obj);
// Perform a simplistic register allocation by merging TMPREG
// partitions with HARDREG "partitions".
unsigned reg = allocate(partition, ordered, life, igraph, p);
if (reg)
{
// reg could not be allocated. Spill the lowest priority
// temporary that has already been allocated.
reg = choose_spill_reg(reg, ordered, spilled);
spill(reg, num_spills, p);
// Add new temporaries to spilled.
for (unsigned i = nregs; i < p.max_reg(); ++i)
spilled.push_back(true);
spilled[reg] = true;
}
else
{
// Write partition data to the TMPREG value structures.
finalize_allocation(partition, p);
done = true;
}
}
}
static void
post_alloc_cleanup (program &p)
{
const unsigned nblocks = p.blocks.size();
unsigned id = 0;
for (unsigned i = 0; i < nblocks; ++i)
{
block *b = p.blocks[i];
for (insn *n, *j = b->first; j != NULL; j = n)
{
n = j->next;
if (j->is_move()
&& j->src1->is_reg()
&& j->dest->reg() == j->src1->reg())
{
// Delete no-op moves created by partition merging.
insn *p = j->prev;
if (p)
p->next = n;
else
b->first = n;
if (n)
n->prev = p;
else
b->last = p;
}
else
{
j->id = id;
// 64-bit immediates take two op slots.
id += ((j->code & 0xff) == (BPF_LD | BPF_IMM | BPF_DW) ? 2 : 1);
}
}
}
}
// XXX PR23860: Passing a short (non-padded) string constant can fail
// the verifier, which is not smart enough to determine that accesses
// past the end of the string will never occur. To fix this, start the
// program with some code to zero out the temporary stack space.
void
zero_stack(program &p)
{
block *entry_block = p.blocks[0];
insn_before_inserter ins(entry_block, entry_block->first, "zero_stack");
value *frame = p.lookup_reg(BPF_REG_10);
for (int32_t ofs = -(int32_t)p.max_tmp_space; ofs < 0; ofs += 4)
p.mk_st(ins, BPF_W, frame, (int32_t)ofs, p.new_imm(0));
}
// XXX: Also zero the spilled registers that are loaded but not saved.
// This is a degenerate case but it happens on some programs with the
// current register allocator:
void
zero_spilled(program &p)
{
block *entry_block = p.blocks[0];
insn_before_inserter ins(entry_block, entry_block->first, "zero_spilled");
value *frame = p.lookup_reg(BPF_REG_10);
for (int32_t ofs = -(int32_t)p.max_reg_space;
ofs < -(int32_t)p.max_tmp_space; ofs += 4)
p.mk_st(ins, BPF_W, frame, (int32_t)ofs, p.new_imm(0));
}
void
program::generate()
{
#ifdef DEBUG_CODEGEN
std::cerr << "DEBUG BEFORE OPT " << *this << std::endl;
#endif
lower_str_values(*this);
zero_stack(*this);
fixup_operands(*this);
thread_jumps(*this);
fold_jumps(*this);
reorder_blocks(*this);
reg_alloc(*this);
zero_spilled(*this);
post_alloc_cleanup(*this);
#ifdef DEBUG_CODEGEN
std::cerr << "DEBUG AFTER OPT " << *this << std::endl;
#endif
}
} // namespace bpf
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