On 02/01/2016 01:52 AM, Maciej W. Rozycki wrote:
> On Fri, 29 Jan 2016, Daniel Wagner wrote:
>
>> Depending on the configuration either the 32 or 64 bit version of
>> elf_check_arch() is defined. parse_crash_elf32_headers() does
>> some basic verification of the ELF header via elf_check_arch().
>> parse_crash_elf64_headers() does it via vmcore_elf64_check_arch()
>> which expands to the same elf_check_check().
>>
>> In file included from include/linux/elf.h:4:0,
>> from fs/proc/vmcore.c:13:
>> fs/proc/vmcore.c: In function 'parse_crash_elf64_headers':
>>>> arch/mips/include/asm/elf.h:228:23: error: initialization from incompatible pointer type [-Werror=incompatible-pointer-types]
>> struct elfhdr *__h = (hdr); \
>> ^
>> include/linux/crash_dump.h:41:37: note: in expansion of macro 'elf_check_arch'
>> #define vmcore_elf64_check_arch(x) (elf_check_arch(x) || vmcore_elf_check_arch_cross(x))
>> ^
>> fs/proc/vmcore.c:1015:4: note: in expansion of macro 'vmcore_elf64_check_arch'
>> !vmcore_elf64_check_arch(&ehdr) ||
>> ^
>>
>> Since the MIPS ELF header for 32 bit and 64 bit differ we need
>> to check accordingly.
>
> I fail to see how it can work as it stands given that `elf_check_arch' is
> called from the same source file both on a pointer to `Elf32_Ehdr' and one
> to `Elf64_Ehdr'. However the MIPS implementations of `elf_check_arch'
> only use an auxiliary variable to avoid multiple evaluation of a macro
> argument and therefore instead I recommend the use of the usual approach
> taken in such a situation within a statement expression, that is to
> declare the variable with `typeof' rather than an explicit type. As an
> upside this will minimise code disruption as well.
Good point on the type for hdr. Thought elf_check_arch() implementation
differ on 32 bit and 64 bit implementation. I played a bit around and the
simplest version I found was this here:
diff --git a/arch/mips/include/asm/elf.h b/arch/mips/include/asm/elf.h
index b01a6ff..8c88238 100644
--- a/arch/mips/include/asm/elf.h
+++ b/arch/mips/include/asm/elf.h
@@ -205,8 +205,6 @@ struct mips_elf_abiflags_v0 {
#define MIPS_ABI_FP_64 6 /* -mips32r2 -mfp64 */
#define MIPS_ABI_FP_64A 7 /* -mips32r2 -mfp64 -mno-odd-spreg */
-#ifdef CONFIG_32BIT
-
/*
* In order to be sure that we don't attempt to execute an O32 binary which
* requires 64 bit FP (FR=1) on a system which does not support it we refuse
@@ -225,23 +223,30 @@ struct mips_elf_abiflags_v0 {
#define elf_check_arch(hdr) \
({ \
int __res = 1; \
- struct elfhdr *__h = (hdr); \
+ typeof(*(hdr)) *__h = (hdr); \
\
if (__h->e_machine != EM_MIPS) \
__res = 0; \
- if (__h->e_ident[EI_CLASS] != ELFCLASS32) \
- __res = 0; \
- if ((__h->e_flags & EF_MIPS_ABI2) != 0) \
- __res = 0; \
- if (((__h->e_flags & EF_MIPS_ABI) != 0) && \
- ((__h->e_flags & EF_MIPS_ABI) != EF_MIPS_ABI_O32)) \
- __res = 0; \
- if (__h->e_flags & __MIPS_O32_FP64_MUST_BE_ZERO) \
- __res = 0; \
+ if (__same_type(hdr, Elf32_Ehdr *)) { \
+ if (__h->e_ident[EI_CLASS] != ELFCLASS32) \
+ __res = 0; \
+ if ((__h->e_flags & EF_MIPS_ABI2) != 0) \
+ __res = 0; \
+ if (((__h->e_flags & EF_MIPS_ABI) != 0) && \
+ ((__h->e_flags & EF_MIPS_ABI) != EF_MIPS_ABI_O32)) \
+ __res = 0; \
+ if (__h->e_flags & __MIPS_O32_FP64_MUST_BE_ZERO) \
+ __res = 0; \
+ } else if (__same_type(hdr, Elf64_Ehdr *)) { \
+ if (__h->e_ident[EI_CLASS] != ELFCLASS64) \
+ __res = 0; \
+ } \
\
__res; \
})
+#ifdef CONFIG_32BIT
+
/*
* These are used to set parameters in the core dumps.
*/
@@ -250,21 +255,6 @@ struct mips_elf_abiflags_v0 {
#endif /* CONFIG_32BIT */
#ifdef CONFIG_64BIT
-/*
- * This is used to ensure we don't load something for the wrong architecture.
- */
-#define elf_check_arch(hdr) \
-({ \
- int __res = 1; \
- struct elfhdr *__h = (hdr); \
- \
- if (__h->e_machine != EM_MIPS) \
- __res = 0; \
- if (__h->e_ident[EI_CLASS] != ELFCLASS64) \
- __res = 0; \
- \
- __res; \
-})
/*
* These are used to set parameters in the core dumps.
Not sure if that is what you had in mind.
cheers,
daniel
