From 17d7194d291bf91d130b78e06cbe27b290e0376d Mon Sep 17 00:00:00 2001 From: Ulf Hermann Date: Fri, 18 Aug 2017 14:05:10 +0200 Subject: [PATCH] Make sure packed structs follow the gcc memory layout gcc defaults to using struct layouts that follow the native conventions, even if __attribute__((packed)) is given. In order to get the layout we expect, we need to tell gcc to always use the gcc struct layout, at least for packed structs. To do this, we can use the gcc_struct attribute. This is important, not only for porting to windows, but also potentially for other platforms, as the bugs resulting from struct layout differences are rather subtle and hard to find. Signed-off-by: Ulf Hermann --- ChangeLog | 5 +++++ backends/ChangeLog | 4 ++++ backends/linux-core-note.c | 2 +- configure.ac | 13 +++++++++++++ lib/ChangeLog | 5 +++++ lib/eu-config.h | 8 ++++++++ libcpu/ChangeLog | 4 ++++ libcpu/memory-access.h | 2 +- libdw/ChangeLog | 4 ++++ libdw/memory-access.h | 2 +- libelf/ChangeLog | 4 ++++ libelf/gelf_xlate.c | 2 +- 12 files changed, 51 insertions(+), 4 deletions(-) diff --git a/ChangeLog b/ChangeLog index c0034ba48..cb87833c3 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,8 @@ +2017-08-18 Ulf Hermann + + * configure.ac: Check if the compiler supports + __attribute__((gcc_struct)). + 2017-09-19 Mark Wielaard * README: Add basic build instructions. diff --git a/backends/ChangeLog b/backends/ChangeLog index 79b50ebf5..8c3f42c60 100644 --- a/backends/ChangeLog +++ b/backends/ChangeLog @@ -1,3 +1,7 @@ +2017-08-18 Ulf Hermann + + * linux-core-note.c: Use attribute_packed. + 2017-04-27 Ulf Hermann * Makefile.am: Use dso_LDFLAGS. diff --git a/backends/linux-core-note.c b/backends/linux-core-note.c index 67638d700..08282ba4d 100644 --- a/backends/linux-core-note.c +++ b/backends/linux-core-note.c @@ -111,7 +111,7 @@ struct EBLHOOK(prstatus) FIELD (INT, pr_fpvalid); } #ifdef ALIGN_PRSTATUS - __attribute__ ((packed, aligned (ALIGN_PRSTATUS))) + attribute_packed __attribute__ ((aligned (ALIGN_PRSTATUS))) #endif ; diff --git a/configure.ac b/configure.ac index fb18dfc8b..4ab8816ad 100644 --- a/configure.ac +++ b/configure.ac @@ -143,6 +143,19 @@ if test "$ac_cv_visibility" = "yes"; then [Defined if __attribute__((visibility())) is supported]) fi +AC_CACHE_CHECK([whether gcc supports __attribute__((gcc_struct))], + ac_cv_gcc_struct, [dnl +save_CFLAGS="$CFLAGS" +CFLAGS="$save_CFLAGS -Werror" +AC_COMPILE_IFELSE([AC_LANG_SOURCE([dnl +struct test { int x; } __attribute__((gcc_struct)); +])], ac_cv_gcc_struct=yes, ac_cv_gcc_struct=no) +CFLAGS="$save_CFLAGS"]) +if test "$ac_cv_gcc_struct" = "yes"; then + AC_DEFINE([HAVE_GCC_STRUCT], [1], + [Defined if __attribute__((gcc_struct)) is supported]) +fi + AC_CACHE_CHECK([whether gcc supports -fPIC], ac_cv_fpic, [dnl save_CFLAGS="$CFLAGS" CFLAGS="$save_CFLAGS -fPIC -Werror" diff --git a/lib/ChangeLog b/lib/ChangeLog index 23c0f41b1..612304538 100644 --- a/lib/ChangeLog +++ b/lib/ChangeLog @@ -1,3 +1,8 @@ +2017-08-18 Ulf Hermann + + * eu-config.h: Define attribute_packed to either + __attribute__((packed)) or __attribute__((packed, gcc_struct)). + 2017-04-27 Ulf Hermann * eu-config.h: Define attribute_hidden to be empty if the compiler diff --git a/lib/eu-config.h b/lib/eu-config.h index 070982828..135803e7a 100644 --- a/lib/eu-config.h +++ b/lib/eu-config.h @@ -75,6 +75,14 @@ #define attribute_hidden /* empty */ #endif +#ifdef HAVE_GCC_STRUCT +#define attribute_packed \ + __attribute__ ((packed, gcc_struct)) +#else +#define attribute_packed \ + __attribute__ ((packed)) +#endif + /* Define ALLOW_UNALIGNED if the architecture allows operations on unaligned memory locations. */ #define SANITIZE_UNDEFINED 1 diff --git a/libcpu/ChangeLog b/libcpu/ChangeLog index 173defe60..c710e5af7 100644 --- a/libcpu/ChangeLog +++ b/libcpu/ChangeLog @@ -1,3 +1,7 @@ +2017-08-18 Ulf Hermann + + * memory-access.h: Use attribute_packed. + 2017-02-27 Ulf Hermann * Makefile.am: Use fpic_CFLAGS. diff --git a/libcpu/memory-access.h b/libcpu/memory-access.h index 44210e2fb..779825fa8 100644 --- a/libcpu/memory-access.h +++ b/libcpu/memory-access.h @@ -90,7 +90,7 @@ union unaligned int16_t s2; int32_t s4; int64_t s8; - } __attribute__ ((packed)); + } attribute_packed; static inline uint16_t read_2ubyte_unaligned (const void *p) diff --git a/libdw/ChangeLog b/libdw/ChangeLog index c13344af2..94e9c9ab0 100644 --- a/libdw/ChangeLog +++ b/libdw/ChangeLog @@ -1,3 +1,7 @@ +2017-08-18 Ulf Hermann + + * memory-access.h: Use attribute_packed. + 2017-02-27 Ulf Hermann * libdwP.h: Use attribute_hidden. diff --git a/libdw/memory-access.h b/libdw/memory-access.h index a749b5a9b..afb651fce 100644 --- a/libdw/memory-access.h +++ b/libdw/memory-access.h @@ -170,7 +170,7 @@ union unaligned int16_t s2; int32_t s4; int64_t s8; - } __attribute__ ((packed)); + } attribute_packed; # define read_2ubyte_unaligned(Dbg, Addr) \ read_2ubyte_unaligned_1 ((Dbg)->other_byte_order, (Addr)) diff --git a/libelf/ChangeLog b/libelf/ChangeLog index 9793d0684..7bd9e1bc0 100644 --- a/libelf/ChangeLog +++ b/libelf/ChangeLog @@ -1,3 +1,7 @@ +2017-08-18 Ulf Hermann + + * gelf_xlate.c: Use attribute_packed. + 2017-04-27 Ulf Hermann * libelfP.h: Use attribute_hidden. diff --git a/libelf/gelf_xlate.c b/libelf/gelf_xlate.c index f3d3b7a06..479f1436e 100644 --- a/libelf/gelf_xlate.c +++ b/libelf/gelf_xlate.c @@ -74,7 +74,7 @@ union unaligned uint16_t u16; uint32_t u32; uint64_t u64; - } __attribute__ ((packed)); + } attribute_packed; #define FETCH(Bits, ptr) (((const union unaligned *) ptr)->u##Bits) #define STORE(Bits, ptr, val) (((union unaligned *) ptr)->u##Bits = val) -- 2.47.2