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[PATCH] stddef: port to pre-C11 GCC on x86
From: |
Paul Eggert |
Subject: |
[PATCH] stddef: port to pre-C11 GCC on x86 |
Date: |
Thu, 2 Apr 2015 10:37:41 -0700 |
On this platform, max_align_t should have an alignment of 8 even
though the storage alignments of double, long, etc. max out at 4.
Inspired by a comment of Andreas Schwab's here:
https://sourceware.org/ml/libc-alpha/2015-04/msg00017.html
* lib/stddef.in.h (_GL_STDDEF_ALIGNAS) [!HAVE_MAX_ALIGN_T]: New macro.
(max_align_t) [!HAVE_MAX_ALIGN_T]: Use it.
* tests/test-stddef.c: Test __alignof__ too, if available.
---
ChangeLog | 11 +++++++++++
lib/stddef.in.h | 19 +++++++++++++++----
tests/test-stddef.c | 10 ++++++++++
3 files changed, 36 insertions(+), 4 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index 41dd857..6d690cc 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,14 @@
+2015-04-02 Paul Eggert <address@hidden>
+
+ stddef: port to pre-C11 GCC on x86
+ On this platform, max_align_t should have an alignment of 8 even
+ though the storage alignments of double, long, etc. max out at 4.
+ Inspired by a comment of Andreas Schwab's here:
+ https://sourceware.org/ml/libc-alpha/2015-04/msg00017.html
+ * lib/stddef.in.h (_GL_STDDEF_ALIGNAS) [!HAVE_MAX_ALIGN_T]: New macro.
+ (max_align_t) [!HAVE_MAX_ALIGN_T]: Use it.
+ * tests/test-stddef.c: Test __alignof__ too, if available.
+
2015-03-24 Pádraig Brady <address@hidden>
quotearg-simple-tests: add missing gl_FUNC_MMAP_ANON dependency
diff --git a/lib/stddef.in.h b/lib/stddef.in.h
index 535132a..d6b81fa 100644
--- a/lib/stddef.in.h
+++ b/lib/stddef.in.h
@@ -83,12 +83,23 @@
/* Some platforms lack max_align_t. */
#if address@hidden@
+/* On the x86, the maximum storage alignment of double, long, etc. is 4,
+ but GCC's C11 ABI for x86 says that max_align_t has an alignment of 8,
+ and the C11 standard allows this. Work around this problem by
+ using __alignof__ (which returns 8 for double) rather than _Alignof
+ (which returns 4), and align each union member accordingly. */
+# ifdef __GNUC__
+# define _GL_STDDEF_ALIGNAS(type) \
+ __attribute__ ((__aligned__ (__alignof__ (type))))
+# else
+# define _GL_STDDEF_ALIGNAS(type) /* */
+# endif
typedef union
{
- char *__p;
- double __d;
- long double __ld;
- long int __i;
+ char *__p _GL_STDDEF_ALIGNAS (char *);
+ double __d _GL_STDDEF_ALIGNAS (double);
+ long double __ld _GL_STDDEF_ALIGNAS (long double);
+ long int __i _GL_STDDEF_ALIGNAS (long int);
} max_align_t;
#endif
diff --git a/tests/test-stddef.c b/tests/test-stddef.c
index 3179496..aa6ae54 100644
--- a/tests/test-stddef.c
+++ b/tests/test-stddef.c
@@ -55,6 +55,16 @@ verify (alignof (ptrdiff_t) <= alignof (max_align_t));
verify (alignof (size_t) <= alignof (max_align_t));
verify (alignof (wchar_t) <= alignof (max_align_t));
verify (alignof (struct d) <= alignof (max_align_t));
+#if defined __GNUC__ || defined __IBM__ALIGNOF__
+verify (__alignof__ (double) <= __alignof__ (max_align_t));
+verify (__alignof__ (int) <= __alignof__ (max_align_t));
+verify (__alignof__ (long double) <= __alignof__ (max_align_t));
+verify (__alignof__ (long int) <= __alignof__ (max_align_t));
+verify (__alignof__ (ptrdiff_t) <= __alignof__ (max_align_t));
+verify (__alignof__ (size_t) <= __alignof__ (max_align_t));
+verify (__alignof__ (wchar_t) <= __alignof__ (max_align_t));
+verify (__alignof__ (struct d) <= __alignof__ (max_align_t));
+#endif
int
main (void)
--
2.1.0
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