Erik Faye-LundSigned integer overflow is not defined in C, so do not depend on it.
This fixes a problem with GCC 4.4.0 and -O3 where the optimizer would consider "consumed_bytes > consumed_bytes + bytes" as a constant expression, and never execute the die()-call.
Signed-off-by: Erik Faye-Lund <kusmabite@gmail.com> --- builtin/index-pack.c | 2 +- builtin/unpack-objects.c | 2 +- git-compat-util.h | 12 ++++++++++++ 3 files changed, 14 insertions(+), 2 deletions(-)
Show changes to 3 files +14 −2
builtin/index-pack.c, builtin/unpack-objects.c, git-compat-util.h
diff --git a/builtin/index-pack.c b/builtin/index-pack.c index 2e680d7..e243d9d 100644 --- a/builtin/index-pack.c +++ b/builtin/index-pack.c @@ -161,7 +161,7 @@ static void use(int bytes) input_offset += bytes; /* make sure off_t is sufficiently large not to wrap */ - if (consumed_bytes > consumed_bytes + bytes) + if (signed_add_overflows(consumed_bytes, bytes)) die("pack too large for current definition of off_t"); consumed_bytes += bytes; } diff --git a/builtin/unpack-objects.c b/builtin/unpack-objects.c index 685566e..f63973c 100644 --- a/builtin/unpack-objects.c +++ b/builtin/unpack-objects.c @@ -83,7 +83,7 @@ static void use(int bytes) offset += bytes; /* make sure off_t is sufficiently large not to wrap */ - if (consumed_bytes > consumed_bytes + bytes) + if (signed_add_overflows(consumed_bytes, bytes)) die("pack too large for current definition of off_t"); consumed_bytes += bytes; } diff --git a/git-compat-util.h b/git-compat-util.h index 81883e7..2af8d3e 100644 --- a/git-compat-util.h +++ b/git-compat-util.h @@ -28,6 +28,18 @@ #define ARRAY_SIZE(x) (sizeof(x)/sizeof(x[0])) #define bitsizeof(x) (CHAR_BIT * sizeof(x)) +#define maximum_signed_value_of_type(a) \ + (INTMAX_MAX >> (bitsizeof(intmax_t) - bitsizeof(a))) + +/* + * Signed integer overflow is undefined in C, so here's a helper macro + * to detect if the sum of two integers will overflow. + * + * Requires: a >= 0, typeof(a) equals typeof(b) + */ +#define signed_add_overflows(a, b) \ + ((b) > maximum_signed_value_of_type(a) - (a)) + #ifdef __GNUC__ #define TYPEOF(x) (__typeof__(x)) #else
-- 1.7.3.1.51.g3f36d.dirty
