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Improve backtraces

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We're now able to rewind the instruction pointer in x86 backtraces. This
helps ensure addr2line cannot print information about unrelated adjacent
code. I've restored -fno-schedule-insns2 in most cases because it really
does cause unpredictable breakage for backtraces.
This commit is contained in:
Justine Tunney 2024-05-30 15:11:45 -07:00
parent cd672e251f
commit 9b6718ac99
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GPG key ID: BE714B4575D6E328
11 changed files with 118 additions and 24 deletions
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50
libc/intrin/describebacktrace.c
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@ -17,34 +17,66 @@
│ PERFORMANCE OF THIS SOFTWARE. │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/intrin/describebacktrace.internal.h"
#include "libc/intrin/iscall.internal.h"
#include "libc/intrin/kprintf.h"
#include "libc/intrin/weaken.h"
#include "libc/log/libfatal.internal.h"
#include "libc/nexgen32e/stackframe.h"
#define N 160
static bool IsDangerous(const void *ptr) {
if (_weaken(kisdangerous))
return _weaken(kisdangerous)(ptr);
return false;
}
static char *FormatHex(char *p, unsigned long x) {
int k = x ? (__builtin_clzl(x) ^ 63) + 1 : 1;
k = (k + 3) & -4;
while (k > 0)
*p++ = "0123456789abcdef"[(x >> (k -= 4)) & 15];
*p = '\0';
return p;
}
dontinstrument const char *(DescribeBacktrace)(char buf[N],
struct StackFrame *fr) {
const struct StackFrame *fr) {
char *p = buf;
char *pe = p + N;
bool gotsome = false;
while (fr) {
if (_weaken(kisdangerous) && _weaken(kisdangerous)(fr)) {
if (IsDangerous(fr)) {
if (p + 1 + 1 + 1 < pe) {
if (gotsome)
*p++ = ' ';
*p = '!';
if (p + 16 + 1 < pe) {
*p++ = ' ';
p = FormatHex(p, (long)fr);
}
}
break;
}
if (p + 16 + 1 + 1 <= pe) {
if (gotsome) {
if (p + 16 + 1 < pe) {
unsigned char *ip = (unsigned char *)fr->addr;
#ifdef __x86_64__
// x86 advances the progrem counter before an instruction
// begins executing. return addresses in backtraces shall
// point to code after the call, which means addr2line is
// going to print unrelated code unless we fixup the addr
if (!IsDangerous(ip))
ip -= __is_call(ip);
#endif
if (gotsome)
*p++ = ' ';
} else {
else
gotsome = true;
}
p = __hexcpy(p, fr->addr);
p = FormatHex(p, (long)ip);
} else {
break;
}
fr = fr->next;
}
*p = 0;
*p = '\0';
return buf;
}