From: Efraim Flashner <efraim@flashner.co.il>
To: Danny Milosavljevic <dannym@scratchpost.org>
Cc: 43591@debbugs.gnu.org, Marius Bakke <marius@gnu.org>
Subject: [bug#43591] [PATCH core-updates] gnu: glibc-final: Catch all cases of a glibc user not requesting 64-bit offsets and then using readdir.
Date: Sun, 27 Sep 2020 09:43:13 +0300 [thread overview]
Message-ID: <20200927064313.GB1386@E5400> (raw)
In-Reply-To: <20200925153646.6ef95908@scratchpost.org>
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On Fri, Sep 25, 2020 at 03:36:46PM +0200, Danny Milosavljevic wrote:
> > >Why is this not an issue with i686 on x86_64 kernels?
> >
> > I'm not sure. I'll check.
>
> $ cat a00.c
> #include <stdio.h>
> #if defined( __ILP32__ )
> #warning ILP32
> #endif
> int main() {
> return sizeof(off_t);
> }
> $ LC_ALL=C guix environment -s i686-linux gcc-toolchain -- gcc -o a00 a00.c
> a00.c:3:2: warning: #warning ILP32 [-Wcpp]
> 3 | #warning ILP32
> | ^~~~~~~
> $ ./a00
> $ echo $?
> 4
>
> That means they are using the Linux kernel's X86_32 ABI.
> It has its own getdents64 system call that returns another value for d_off.
>
> $ LC_ALL=C guix environment -s i686-linux gcc-toolchain -- gcc -o a00 -D_FILE_OFFSET_BITS=64 a00.c
> a00.c:3:2: warning: #warning ILP32 [-Wcpp]
> 3 | #warning ILP32
> | ^~~~~~~
> $ ./a00
> $ echo $?
> 8
>
> That is why __i686__ is not affected--at the cost of the kernel lying to us
> about the file system.
>
> Note that I also tried printing the actual d_off values[1]--on ILP32, even with
> _FILE_OFFSET_BITS=64, the VALUES are still 32 bits, and the same values as
> without _FILE_OFFSET_BITS. The d_off SLOT gets bigger on _FILE_OFFSET_BITS=64.
>
> (I also tried printing the actual d_off values[1] on x86_64 without any guix
> environment -s, I get entirely different d_off values!!)
>
> I also tried the former on native ARMHF--you get 32 bits d_off values. And d_off
> is always the same size as off_t.
>
> off_t size changes depending on _FILE_OFFSET_BITS.
>
> I do not have access to a real aarch64 machine--so no idea how it is there.
> That would be the most interesting case, because those don't have X86_32,
> so ILP32 is either not present or implemented differently.
>
> ppc64 would also be interesting...
>
> Test result of [1]:
>
> system _FILE_OFFSET_BITS off_t d_off-sizeof d_off-values
> -------------------------------------------------------------
> x86_64 - 8 Byte 8 Byte 8 Byte
> i686 - 4 Byte 4 Byte 4 Byte
> i686 64 8 Byte 8 Byte 4 Byte
> i686 32 4 Byte 4 Byte 4 Byte
> i686 7 4 Byte 4 Byte 4 Byte
> armhf - 4 Byte 4 Byte 4 Byte
> armhf 64 8 Byte 8 Byte 4 Byte
> armhf 32 4 Byte 4 Byte 4 Byte
> armhf 7 4 Byte 4 Byte 4 Byte
>
> This is all without qemu--in order to simplify the test case.
>
> So I take it ext4 has some special compilation mode for 32 bits...
>
> Could someone please test [1] on (real!) aarch64 and ppc64 and ppc32
> machines?
>
> [1] $ cat a00.c
> #include <stdio.h>
> #include <errno.h>
> #include <assert.h>
> #include <dirent.h>
> #if defined( __ILP32__ )
> #warning ILP32
> #endif
>
> int main() {
> DIR* d;
> struct dirent* ent;
> d = opendir("/tmp");
> errno = 0;
> assert(sizeof(ent->d_off) == sizeof(off_t));
> while ((ent = readdir(d)) != NULL) {
> printf("%llu\n", (unsigned long long) ent->d_off);
> }
> if (errno)
> perror("readdir");
> return sizeof(off_t);
missing } at the end
tested on my ibook G4:
(I believe for powerpc the 32-bit is defined as __powerpc__)
(ins)efraim@g4:~$ gcc -o a00 a00.c
(ins)efraim@g4:~$ ./a00
404218588
473424804
681064434
708508942
805784207
980330722
1080794671
1734802884
1909818320
1923689764
2019671154
2125602108
2147483647
(ins)efraim@g4:~$ echo $?
4
(ins)efraim@g4:~$ rm a00
(ins)efraim@g4:~$ gcc -o a00 -D_FILE_OFFSET_BITS=64 a00.c
(ins)efraim@g4:~$ ./a00
404218588
473424804
681064434
708508942
805784207
980330722
1080794671
1734802884
1909818320
1923689764
2019671154
2125602108
2147483647
(ins)efraim@g4:~$ echo $?
8
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Efraim Flashner <efraim@flashner.co.il> אפרים פלשנר
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next prev parent reply other threads:[~2020-09-27 6:57 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-24 14:12 [bug#43591] [PATCH core-updates] gnu: glibc-final: Catch all cases of a glibc user not requesting 64-bit offsets and then using readdir Danny Milosavljevic
2020-09-24 14:16 ` Danny Milosavljevic
2020-09-24 18:17 ` Marius Bakke
2020-09-24 20:27 ` Danny Milosavljevic
2020-09-24 23:11 ` Marius Bakke
2020-09-25 10:20 ` Danny Milosavljevic
2020-09-25 10:42 ` [bug#43591] [PATCH v2 core-updates] gnu: glibc-final: Catch all cases of a glibc user not requesting 64-bit offsets and then using readdir regardless Danny Milosavljevic
2020-09-25 13:36 ` [bug#43591] [PATCH core-updates] gnu: glibc-final: Catch all cases of a glibc user not requesting 64-bit offsets and then using readdir Danny Milosavljevic
2020-09-25 15:33 ` Danny Milosavljevic
2020-09-26 1:42 ` Danny Milosavljevic
2020-09-26 1:49 ` Danny Milosavljevic
2020-09-29 14:51 ` Danny Milosavljevic
2020-09-27 6:43 ` Efraim Flashner [this message]
2020-09-25 20:03 ` Andreas Enge
2020-09-26 10:50 ` Danny Milosavljevic
2020-09-29 20:52 ` Ludovic Courtès
2020-09-29 22:09 ` Danny Milosavljevic
2020-09-30 9:32 ` Ludovic Courtès
2020-09-30 10:28 ` Danny Milosavljevic
2020-10-01 7:14 ` Ludovic Courtès
2020-10-02 7:18 ` Danny Milosavljevic
2020-10-02 8:12 ` Danny Milosavljevic
2020-10-02 9:47 ` Danny Milosavljevic
2020-10-02 9:32 ` Danny Milosavljevic
2020-10-06 15:39 ` Danny Milosavljevic
2020-09-25 10:24 ` Danny Milosavljevic
2020-09-30 8:45 ` [bug#43591] [PATCH core-updates v2 0/5] " Danny Milosavljevic
2020-09-30 8:45 ` [bug#43591] [PATCH core-updates v2 1/5] gnu: glibc-final: Catch all cases of a glibc user not requesting 64-bit offsets and then using readdir regardless Danny Milosavljevic
2020-09-30 16:55 ` Danny Milosavljevic
2020-09-30 8:45 ` [bug#43591] [PATCH core-updates v2 2/5] build-system/gnu: Explicity declare the _FILE_OFFSET_BITS we want Danny Milosavljevic
2020-09-30 8:45 ` [bug#43591] [PATCH core-updates v2 3/5] gnu: glibc: Do not explicitly set _FILE_OFFSET_BITS Danny Milosavljevic
2020-09-30 8:45 ` [bug#43591] [PATCH core-updates v2 4/5] gnu: glibc-mesboot0: " Danny Milosavljevic
2020-09-30 8:45 ` [bug#43591] [PATCH core-updates v2 5/5] gnu: rhash: Explicity declare the _FILE_OFFSET_BITS we want Danny Milosavljevic
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