Re: C++ conversion status update
Pedro Alves <[email protected]>
| Newsgroups | gmane.comp.gdb.devel |
|---|---|
| Message-ID | <[email protected]> |
On 12/15/2015 08:02 PM, Simon Marchi wrote: > On 15 December 2015 at 06:46, Jose E. Marchesi <[email protected]> wrote: >> g++ -g -O2 -I. -I../../gdb -I../../gdb/common -I../../gdb/config -DLOCALEDIR="\"/usr/local/share/locale\"" -DHAVE_CONFIG_H -I../../gdb/../include/opcode -I../../gdb/../opcodes/.. -I../../gdb/../readline/.. -I../../gdb/../zlib -I../bfd -I../../gdb/../bfd -I../../gdb/../include -I../libdecnumber -I../../gdb/../libdecnumber -I../../gdb/gnulib/import -Ibuild-gnulib/import -DTUI=1 -I/usr/include/python2.6 -I/usr/include/python2.6 -Wall -Wpointer-arith -Wno-unused -Wunused-value -Wunused-function -Wno-switch -Wno-char-subscripts -Wempty-body -Wno-sign-compare -Wno-write-strings -Wno-narrowing -Wformat-nonliteral -Werror -c -o sparc64-tdep.o -MT sparc64-tdep.o -MMD -MP -MF .deps/sparc64-tdep.Tpo ../../gdb/sparc64-tdep.c >> cc1plus: warnings being treated as errors >> In file included from ../../gdb/target.h:74, >> from ../../gdb/exec.h:23, >> from ../../gdb/gdbcore.h:29, >> from ../../gdb/sparc64-tdep.c:27: >> ../../gdb/btrace.h: In function ‘size_t VEC_btrace_insn_s_embedded_size(int)’: >> ../../gdb/btrace.h:84: error: invalid access to non-static data member ‘VEC_btrace_insn_s::vec’ of NULL object >> ../../gdb/btrace.h:84: error: (perhaps the ‘offsetof’ macro was used incorrectly) >> ../../gdb/btrace.h: In function ‘VEC_btrace_insn_s* VEC_btrace_insn_s_alloc(int)’: >> ../../gdb/btrace.h:84: error: invalid access to non-static data member ‘VEC_btrace_insn_s::vec’ of NULL object >> ../../gdb/btrace.h:84: error: (perhaps the ‘offsetof’ macro was used incorrectly) >> ../../gdb/btrace.h: In function ‘VEC_btrace_insn_s* VEC_btrace_insn_s_copy(VEC_btrace_insn_s*)’: >> ../../gdb/btrace.h:84: error: invalid access to non-static data member ‘VEC_btrace_insn_s::vec’ of NULL object >> ../../gdb/btrace.h:84: error: (perhaps the ‘offsetof’ macro was used incorrectly) >> ../../gdb/btrace.h: In function ‘VEC_btrace_insn_s* VEC_btrace_insn_s_merge(VEC_btrace_insn_s*, VEC_btrace_insn_s*)’: >> ../../gdb/btrace.h:84: error: invalid access to non-static data member ‘VEC_btrace_insn_s::vec’ of NULL object >> ../../gdb/btrace.h:84: error: (perhaps the ‘offsetof’ macro was used incorrectly) >> ../../gdb/btrace.h: In function ‘int VEC_btrace_insn_s_reserve(VEC_btrace_insn_s**, int, const char*, unsigned int)’: >> ../../gdb/btrace.h:84: error: invalid access to non-static data member ‘VEC_btrace_insn_s::vec’ of NULL object >> ../../gdb/btrace.h:84: error: (perhaps the ‘offsetof’ macro was used incorrectly) >> At global scope: >> cc1plus: error: unrecognized command line option "-Wno-narrowing" >> make[2]: *** [sparc64-tdep.o] Error 1 >> make[2]: Leaving directory `/home/jemarch/couts2/binutils-gdb/build/gdb' >> make[1]: *** [all-gdb] Error 2 >> make[1]: Leaving directory `/home/jemarch/couts2/binutils-gdb/build' >> make: *** [all] Error 2 > > This can be reproduced with g++ 4.4 on any architecture, i think. > > This seems to be caused by the interaction of enum_flags and the > vector implementation. After preprocessing we have this: > > __builtin_offsetof (VEC_btrace_insn_s, vec) > > However, VEC_btrace_insn_s is a non-POD data type, because it > ultimately contains an enum_flags object, which is non-POD. > > VEC_btrace_insn_s > btrace_insn_s vec[1]; > btrace_insn_flags flags; (enum_flags <enum btrace_insn_flag>) > > From what I read, using offsetof on a non-POD structure is an > undefined behavior, at least in C++98. I don't know if it has changed > in later standard versions, but later g++ do not complain. Yeah, C++11 relaxed the rules a lot. enum_flags is designed to be POD-like, though it has user-defined constructors. It's quite safe to memcpy it. > > For g++ 4.4, it is possible to silence the warning/error with > -Wno-invalid-offsetof, if we know that it still produces good results. > Yeah, it should work. The real fix of course would be to reimplement vec.h using real C++ templates (until we can get rid of C mode, that is). An alternative is to avoid offsetof in the code itself, like in the patch below. It's really offsetof-but-avoid-NULL. An advantage over disabling the warning is that it's contained in the VEC code, which lets G++ catch issues elsewhere. OTOH, disabling warning is simpler. WDYT? From c0803a1aca62cde14c47a103aa996f1e1f4a2875 Mon Sep 17 00:00:00 2001 From: Pedro Alves <[email protected]> Date: Tue, 15 Dec 2015 22:43:06 +0000 Subject: [PATCH] no offsetof --- gdb/common/vec.h | 44 ++++++++++++++++++++++++++++++++++---------- 1 file changed, 34 insertions(+), 10 deletions(-) diff --git a/gdb/common/vec.h b/gdb/common/vec.h index 6189283..a188b02 100644 --- a/gdb/common/vec.h +++ b/gdb/common/vec.h @@ -437,13 +437,23 @@ DEF_VEC_FUNC_O(T) \ DEF_VEC_ALLOC_FUNC_O(T) \ struct vec_swallow_trailing_semi +/* Avoid offsetof (or its usual C implementation) as it triggers + -Winvalid-offsetof warnings with enum_flags types with G++ <= 4.4, + even though those types are memcpyable. This requires allocating a + dummy local VEC in all routines that use this, but that has the + advantage that it only works if T is default constructible, which + is exactly a check we want, to keep C compatibility. */ +#define vec_offset(T, VPTR) ((size_t) ((char *) &(VPTR)->vec - (char *) VPTR)) + #define DEF_VEC_ALLOC_FUNC_I(T) \ static inline VEC(T) *VEC_OP (T,alloc) \ (int alloc_) \ { \ + VEC(T) dummy; \ + \ /* We must request exact size allocation, hence the negation. */ \ return (VEC(T) *) vec_o_reserve (NULL, -alloc_, \ - offsetof (VEC(T),vec), sizeof (T)); \ + vec_offset (T, &dummy), sizeof (T)); \ } \ \ static inline VEC(T) *VEC_OP (T,copy) (VEC(T) *vec_) \ @@ -453,9 +463,11 @@ static inline VEC(T) *VEC_OP (T,copy) (VEC(T) *vec_) \ \ if (len_) \ { \ + VEC(T) dummy; \ + \ /* We must request exact size allocation, hence the negation. */ \ new_vec_ = (VEC (T) *) \ - vec_o_reserve (NULL, -len_, offsetof (VEC(T),vec), sizeof (T)); \ + vec_o_reserve (NULL, -len_, vec_offset (T, &dummy), sizeof (T)); \ \ new_vec_->num = len_; \ memcpy (new_vec_->vec, vec_->vec, sizeof (T) * len_); \ @@ -467,12 +479,13 @@ static inline VEC(T) *VEC_OP (T,merge) (VEC(T) *vec1_, VEC(T) *vec2_) \ { \ if (vec1_ && vec2_) \ { \ + VEC(T) dummy; \ size_t len_ = vec1_->num + vec2_->num; \ VEC (T) *new_vec_ = NULL; \ \ /* We must request exact size allocation, hence the negation. */ \ new_vec_ = (VEC (T) *) \ - vec_o_reserve (NULL, -len_, offsetof (VEC(T),vec), sizeof (T)); \ + vec_o_reserve (NULL, -len_, vec_offset (T, &dummy), sizeof (T)); \ \ new_vec_->num = len_; \ memcpy (new_vec_->vec, vec1_->vec, sizeof (T) * vec1_->num); \ @@ -505,12 +518,13 @@ static inline void VEC_OP (T,cleanup) \ static inline int VEC_OP (T,reserve) \ (VEC(T) **vec_, int alloc_ VEC_ASSERT_DECL) \ { \ + VEC(T) dummy; \ int extend = !VEC_OP (T,space) \ (*vec_, alloc_ < 0 ? -alloc_ : alloc_ VEC_ASSERT_PASS); \ \ if (extend) \ *vec_ = (VEC(T) *) vec_o_reserve (*vec_, alloc_, \ - offsetof (VEC(T),vec), sizeof (T)); \ + vec_offset (T, &dummy), sizeof (T)); \ \ return extend; \ } \ @@ -581,7 +595,9 @@ static inline int VEC_OP (T,iterate) \ static inline size_t VEC_OP (T,embedded_size) \ (int alloc_) \ { \ - return offsetof (VEC(T),vec) + alloc_ * sizeof(T); \ + VEC(T) dummy; \ + \ + return vec_offset (T, &dummy) + alloc_ * sizeof(T); \ } \ \ static inline void VEC_OP (T,embedded_init) \ @@ -863,7 +879,9 @@ static inline int VEC_OP (T,iterate) \ static inline size_t VEC_OP (T,embedded_size) \ (int alloc_) \ { \ - return offsetof (VEC(T),vec) + alloc_ * sizeof(T); \ + VEC(T) dummy; \ + \ + return vec_offset (T, &dummy) + alloc_ * sizeof(T); \ } \ \ static inline void VEC_OP (T,embedded_init) \ @@ -998,9 +1016,11 @@ static inline unsigned VEC_OP (T,lower_bound) \ static inline VEC(T) *VEC_OP (T,alloc) \ (int alloc_) \ { \ + VEC(T) dummy; \ + \ /* We must request exact size allocation, hence the negation. */ \ return (VEC(T) *) vec_o_reserve (NULL, -alloc_, \ - offsetof (VEC(T),vec), sizeof (T)); \ + vec_offset (T, &dummy), sizeof (T)); \ } \ \ static inline VEC(T) *VEC_OP (T,copy) (VEC(T) *vec_) \ @@ -1010,9 +1030,11 @@ static inline VEC(T) *VEC_OP (T,copy) (VEC(T) *vec_) \ \ if (len_) \ { \ + VEC(T) dummy; \ + \ /* We must request exact size allocation, hence the negation. */ \ new_vec_ = (VEC (T) *) \ - vec_o_reserve (NULL, -len_, offsetof (VEC(T),vec), sizeof (T)); \ + vec_o_reserve (NULL, -len_, vec_offset (T, &dummy), sizeof (T)); \ \ new_vec_->num = len_; \ memcpy (new_vec_->vec, vec_->vec, sizeof (T) * len_); \ @@ -1024,12 +1046,13 @@ static inline VEC(T) *VEC_OP (T,merge) (VEC(T) *vec1_, VEC(T) *vec2_) \ { \ if (vec1_ && vec2_) \ { \ + VEC(T) dummy; \ size_t len_ = vec1_->num + vec2_->num; \ VEC (T) *new_vec_ = NULL; \ \ /* We must request exact size allocation, hence the negation. */ \ new_vec_ = (VEC (T) *) \ - vec_o_reserve (NULL, -len_, offsetof (VEC(T),vec), sizeof (T)); \ + vec_o_reserve (NULL, -len_, vec_offset (T, &dummy), sizeof (T)); \ \ new_vec_->num = len_; \ memcpy (new_vec_->vec, vec1_->vec, sizeof (T) * vec1_->num); \ @@ -1062,12 +1085,13 @@ static inline void VEC_OP (T,cleanup) \ static inline int VEC_OP (T,reserve) \ (VEC(T) **vec_, int alloc_ VEC_ASSERT_DECL) \ { \ + VEC(T) dummy; \ int extend = !VEC_OP (T,space) (*vec_, alloc_ < 0 ? -alloc_ : alloc_ \ VEC_ASSERT_PASS); \ \ if (extend) \ *vec_ = (VEC(T) *) \ - vec_o_reserve (*vec_, alloc_, offsetof (VEC(T),vec), sizeof (T)); \ + vec_o_reserve (*vec_, alloc_, vec_offset (T, &dummy), sizeof (T)); \ \ return extend; \ } \ -- 1.9.3