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Fix boundschecking for signal/sigaction/fork

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The BOUNDS_CHECKING_ON/BOUNDS_CHECKING_OFF is not working for
signal/sigaction/fork. The reason is that the code stops bound checking
for the whole application. This result in wrong handling of
__bound_local_new/__bound_local_delete and malloc/calloc/realloc/free.
Consider the following code:

void tst(int n) {
  int i, arr[n];
  for (i = 0; i < n; i++) arr[i] = 0;
}

void *some_thread(void *dummy) {
  while (running) { tst(10); tst(20); }
}

void signal_handler(int sig) { ... }

When the signal handler is called the some_thread code can be interrupted when
is just registered the arr[10] data. When the signal handler is leaved the
arr[10] is still registered and did not see the call to deregister arr[10] and
then register arr[20]. The code resumes when tst(20) is running. This results
in a bound checking error when i >= 10.

To solve the above problem I changed the bound checking code to use
tls (thread local storage) for the no_checking variable.
This also makes it now possible to redirect signal/sigaction/fork code
through the bound checking library and disable checking when a signal is
running and to correct the bounds_sem for the fork child process.
The BOUNDS_CHECKING_ON/BOUNDS_CHECKING_OFF is not needed any more for
signal/sigaction/fork. In fact I could remove them from all my applications.

The use of the tls function code slows down the code by about 10%.
So if the slowdown due to bound checking was 5. It is now 5.5 times slower.

For x86_64/i386 I also allowed to use __thread variable in bcheck.c when
compiled with gcc with:
make x86_64-libtcc1-usegcc=yes
make i386-libtcc1-usegcc=yes
This makes code run faster due to use of gcc and __thread variable.
With the __thread variable there is no 10% slowdown.
For other targets this does not work because stabs is not supported.

Changes:

lib/bcheck.c:
- Add TRY_SEM
- Add HAVE_SIGNAL/HAVE_SIGACTION/HAVE_FORK/HAVE_TLS_FUNC/HAVE_TLS_VAR
  - HAVE_SIGNAL: redirect signal() call if set.
  - HAVE_SIGACTION: redirect sigaction() call if set.
  - HAVE_FORK: redirect fork() call if set.
  - HAVE_TLS_FUNC: If target has tls function calls.
  - HAVE_TLS_VAR: If target has __thread tls support.
- Replace all no_checking refecrences to NO_CHECKING_SET/NO_CHECKING_GET macros

tcc-doc.texi:
- Remove examples for signal/sigaction/fork code.
- Add some explanation for signal/sigaction/fork code.
- Add documentaion for __bounds_checking().

tccelf.c:
- Add support for SHF_TLS

tests/tests2/114_bound_signal.c:
- Remove BOUNDS_CHECKING_ON/BOUNDS_CHECKING_OFF
- Add code to trigger failure when tls is not working.

x86_64-link.c:
- Add support for R_X86_64_TLSGD/R_X86_64_TLSLD/R_X86_64_DTPOFF32/R_X86_64_TPOFF32

i386-link.c:
- Add support for R_386_TLS_GD/R_386_TLS_LDM/R_386_TLS_LDO_32/R_386_TLS_LE
This commit is contained in:
herman ten brugge
2020-09-08 14:31:58 +02:00
parent 53d815b8a0
commit 853a498f2c
6 changed files with 529 additions and 122 deletions
Download Patch File Download Diff File Expand all files Collapse all files

72
x86_64-link.c
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@@ -43,6 +43,10 @@ int code_reloc (int reloc_type)
case R_X86_64_COPY:
case R_X86_64_RELATIVE:
case R_X86_64_GOTOFF64:
case R_X86_64_TLSGD:
case R_X86_64_TLSLD:
case R_X86_64_DTPOFF32:
case R_X86_64_TPOFF32:
return 0;
case R_X86_64_PC32:
@@ -87,6 +91,10 @@ int gotplt_entry_type (int reloc_type)
case R_X86_64_GOTOFF64:
case R_X86_64_GOTPCREL:
case R_X86_64_GOTPCRELX:
case R_X86_64_TLSGD:
case R_X86_64_TLSLD:
case R_X86_64_DTPOFF32:
case R_X86_64_TPOFF32:
case R_X86_64_REX_GOTPCRELX:
case R_X86_64_PLT32:
case R_X86_64_PLTOFF64:
@@ -281,6 +289,70 @@ void relocate(TCCState *s1, ElfW_Rel *rel, int type, unsigned char *ptr, addr_t
case R_X86_64_GOTOFF64:
add64le(ptr, val - s1->got->sh_addr);
break;
case R_X86_64_TLSGD:
{
static const unsigned char expect[] = {
/* .byte 0x66; lea 0(%rip),%rdi */
0x66, 0x48, 0x8d, 0x3d, 0x00, 0x00, 0x00, 0x00,
/* .word 0x6666; rex64; call __tls_get_addr@PLT */
0x66, 0x66, 0x48, 0xe8, 0x00, 0x00, 0x00, 0x00 };
static const unsigned char replace[] = {
/* mov %fs:0,%rax */
0x64, 0x48, 0x8b, 0x04, 0x25, 0x00, 0x00, 0x00, 0x00,
/* lea -4(%rax),%rax */
0x48, 0x8d, 0x80, 0x00, 0x00, 0x00, 0x00 };
if (memcmp (ptr-4, expect, sizeof(expect)) == 0) {
ElfW(Sym) *sym;
Section *sec;
int32_t x;
memcpy(ptr-4, replace, sizeof(replace));
rel[1].r_info = ELFW(R_INFO)(0, R_X86_64_NONE);
sym = &((ElfW(Sym) *)symtab_section->data)[sym_index];
sec = s1->sections[sym->st_shndx];
x = sym->st_value - sec->sh_addr - sec->data_offset;
add32le(ptr + 8, x);
}
else
tcc_error("unexpected R_X86_64_TLSGD pattern");
}
break;
case R_X86_64_TLSLD:
{
static const unsigned char expect[] = {
/* lea 0(%rip),%rdi */
0x48, 0x8d, 0x3d, 0x00, 0x00, 0x00, 0x00,
/* call __tls_get_addr@PLT */
0xe8, 0x00, 0x00, 0x00, 0x00 };
static const unsigned char replace[] = {
/* data16 data16 data16 mov %fs:0,%rax */
0x66, 0x66, 0x66, 0x64, 0x48, 0x8b, 0x04, 0x25,
0x00, 0x00, 0x00, 0x00 };
if (memcmp (ptr-3, expect, sizeof(expect)) == 0) {
memcpy(ptr-3, replace, sizeof(replace));
rel[1].r_info = ELFW(R_INFO)(0, R_X86_64_NONE);
}
else
tcc_error("unexpected R_X86_64_TLSLD pattern");
}
break;
case R_X86_64_DTPOFF32:
case R_X86_64_TPOFF32:
{
ElfW(Sym) *sym;
Section *sec;
int32_t x;
sym = &((ElfW(Sym) *)symtab_section->data)[sym_index];
sec = s1->sections[sym->st_shndx];
x = val - sec->sh_addr - sec->data_offset;
add32le(ptr, x);
}
break;
case R_X86_64_NONE:
break;
case R_X86_64_RELATIVE:
#ifdef TCC_TARGET_PE
add32le(ptr, val - s1->pe_imagebase);