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authorSiddhesh Poyarekar <siddhesh@sourceware.org>2020-12-30 11:54:00 +0530
committerSiddhesh Poyarekar <siddhesh@sourceware.org>2020-12-31 16:55:21 +0530
commitc43c5796121bc5bcc0867f02e5536874aa8196c1 (patch)
tree39306f12f031a62b0fe2ca679e656332e70eb388 /include
parent2a08b6e8331a611dc29325bfa6e29fecc9a3a46e (diff)
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Introduce _FORTIFY_SOURCE=3
Introduce a new _FORTIFY_SOURCE level of 3 to enable additional fortifications that may have a noticeable performance impact, allowing more fortification coverage at the cost of some performance. With llvm 9.0 or later, this will replace the use of __builtin_object_size with __builtin_dynamic_object_size. __builtin_dynamic_object_size ----------------------------- __builtin_dynamic_object_size is an LLVM builtin that is similar to __builtin_object_size. In addition to what __builtin_object_size does, i.e. replace the builtin call with a constant object size, __builtin_dynamic_object_size will replace the call site with an expression that evaluates to the object size, thus expanding its applicability. In practice, __builtin_dynamic_object_size evaluates these expressions through malloc/calloc calls that it can associate with the object being evaluated. A simple motivating example is below; -D_FORTIFY_SOURCE=2 would miss this and emit memcpy, but -D_FORTIFY_SOURCE=3 with the help of __builtin_dynamic_object_size is able to emit __memcpy_chk with the allocation size expression passed into the function: void *copy_obj (const void *src, size_t alloc, size_t copysize) { void *obj = malloc (alloc); memcpy (obj, src, copysize); return obj; } Limitations ----------- If the object was allocated elsewhere that the compiler cannot see, or if it was allocated in the function with a function that the compiler does not recognize as an allocator then __builtin_dynamic_object_size also returns -1. Further, the expression used to compute object size may be non-trivial and may potentially incur a noticeable performance impact. These fortifications are hence enabled at a new _FORTIFY_SOURCE level to allow developers to make a choice on the tradeoff according to their environment.
Diffstat (limited to 'include')
-rw-r--r--include/features.h5
1 files changed, 5 insertions, 0 deletions
diff --git a/include/features.h b/include/features.h
index 540230b..066eb0e 100644
--- a/include/features.h
+++ b/include/features.h
@@ -397,6 +397,11 @@
# warning _FORTIFY_SOURCE requires compiling with optimization (-O)
# elif !__GNUC_PREREQ (4, 1)
# warning _FORTIFY_SOURCE requires GCC 4.1 or later
+# elif _FORTIFY_SOURCE > 2 && __glibc_clang_prereq (9, 0)
+# if _FORTIFY_SOURCE > 3
+# warning _FORTIFY_SOURCE > 3 is treated like 3 on this platform
+# endif
+# define __USE_FORTIFY_LEVEL 3
# elif _FORTIFY_SOURCE > 1
# if _FORTIFY_SOURCE > 2
# warning _FORTIFY_SOURCE > 2 is treated like 2 on this platform