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FORTIFY_SOURCE: optimize

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Don't do the fortify_source checks if we can determine, at
compile time, that the provided operation is safe.

This avoids silliness like calling fortify source on things like:

  size_t len = strlen("asdf");
  printf("%d\n", len);

and allows the compiler to optimize this code to:

  printf("%d\n", 4);

Defer to gcc's builtin functions instead of pointing our code
to the libc implementation.

Change-Id: I5e1dcb61946461c4afaaaa983e39f07c7a0df0ae
This commit is contained in:
Nick Kralevich 2013-01-17 15:41:33 -08:00
parent f3fe19459f
commit a44e9afdd1
2 changed files with 39 additions and 9 deletions
libc/include
string.h
tests
string_test.cpp

27
libc/include/string.h

@ -201,8 +201,6 @@ size_t strlcat(char *dest, const char *src, size_t size) {
return __strlcat_chk(dest, src, size, bos);
}
__purefunc extern size_t __strlen_real(const char *)
__asm__(__USER_LABEL_PREFIX__ "strlen");
extern size_t __strlen_chk(const char *, size_t);
__BIONIC_FORTIFY_INLINE
@ -211,14 +209,17 @@ size_t strlen(const char *s) {
// Compiler doesn't know destination size. Don't call __strlen_chk
if (bos == __BIONIC_FORTIFY_UNKNOWN_SIZE) {
return __strlen_real(s);
return __builtin_strlen(s);
}
size_t slen = __builtin_strlen(s);
if (__builtin_constant_p(slen)) {
return slen;
}
return __strlen_chk(s, bos);
}
__purefunc extern char* __strchr_real(const char *, int)
__asm__(__USER_LABEL_PREFIX__ "strchr");
extern char* __strchr_chk(const char *, int, size_t);
__BIONIC_FORTIFY_INLINE
@ -227,14 +228,17 @@ char* strchr(const char *s, int c) {
// Compiler doesn't know destination size. Don't call __strchr_chk
if (bos == __BIONIC_FORTIFY_UNKNOWN_SIZE) {
return __strchr_real(s, c);
return __builtin_strchr(s, c);
}
size_t slen = __builtin_strlen(s);
if (__builtin_constant_p(slen) && (slen < bos)) {
return __builtin_strchr(s, c);
}
return __strchr_chk(s, c, bos);
}
__purefunc extern char* __strrchr_real(const char *, int)
__asm__(__USER_LABEL_PREFIX__ "strrchr");
extern char* __strrchr_chk(const char *, int, size_t);
__BIONIC_FORTIFY_INLINE
@ -243,7 +247,12 @@ char* strrchr(const char *s, int c) {
// Compiler doesn't know destination size. Don't call __strrchr_chk
if (bos == __BIONIC_FORTIFY_UNKNOWN_SIZE) {
return __strrchr_real(s, c);
return __builtin_strrchr(s, c);
}
size_t slen = __builtin_strlen(s);
if (__builtin_constant_p(slen) && (slen < bos)) {
return __builtin_strrchr(s, c);
}
return __strrchr_chk(s, c, bos);

21
tests/string_test.cpp

@ -316,6 +316,27 @@ TEST(string_DeathTest, strcpy_fortified) {
ASSERT_EXIT(strcpy(buf, orig), testing::KilledBySignal(SIGSEGV), "");
free(orig);
}
TEST(string_DeathTest, strlen_fortified) {
::testing::FLAGS_gtest_death_test_style = "threadsafe";
char buf[10];
memcpy(buf, "0123456789", sizeof(buf));
ASSERT_EXIT(printf("%d", strlen(buf)), testing::KilledBySignal(SIGSEGV), "");
}
TEST(string_DeathTest, strchr_fortified) {
::testing::FLAGS_gtest_death_test_style = "threadsafe";
char buf[10];
memcpy(buf, "0123456789", sizeof(buf));
ASSERT_EXIT(printf("%s", strchr(buf, 'a')), testing::KilledBySignal(SIGSEGV), "");
}
TEST(string_DeathTest, strrchr_fortified) {
::testing::FLAGS_gtest_death_test_style = "threadsafe";
char buf[10];
memcpy(buf, "0123456789", sizeof(buf));
ASSERT_EXIT(printf("%s", strrchr(buf, 'a')), testing::KilledBySignal(SIGSEGV), "");
}
#endif
#if __BIONIC__