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Message-ID: <dab9357bd21d257f66a9f6a145570d0de61c4595.camel@xry111.site>
Date: Wed, 21 Aug 2024 15:52:31 +0800
From: Xi Ruoyao <xry111@...111.site>
To: Huacai Chen <chenhuacai@...nel.org>, Tiezhu Yang
<yangtiezhu@...ngson.cn>, Jinyang He <hejinyang@...ngson.cn>
Cc: Arnd Bergmann <arnd@...db.de>, loongarch@...ts.linux.dev,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/2] LoongArch: Define barrier_before_unreachable()
as empty
On Wed, 2024-08-21 at 15:37 +0800, Huacai Chen wrote:
> > I am not sure whether the GCC bug has been fixed, I can not find the
> > fixup in the link https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82365
> > and in the GCC repo. So I am not sure whether it is time and proper
> > to remove this workaround in the common header totally, just remove
> > it in the arch specified header when compiling kernel with a newer
> > GCC version (for example GCC 12.1 or higher on LoongArch) at least.
> What's your opinion? From my point of view, this GCC bug hasn't been
> fixed. So there may still be potential problems.
I'm pretty sure it isn't fixed. Using the test case from the bug
report:
struct i2c_board_info {
char type[20];
char pad[100];
};
#ifdef NONORETURN
void fortify_panic();
#else
void fortify_panic() __attribute__((noreturn));
#endif
int f(int a)
{
if (a)
fortify_panic();
}
void i2c_new_device(struct i2c_board_info *);
int em28xx_dvb_init(int model, int a, int b, int c, int d)
{
switch (model) {
case 1:{
struct i2c_board_info info = {};
f(a);
i2c_new_device(&info);
break;
}
case 2:{
struct i2c_board_info info = {};
f(b);
i2c_new_device(&info);
break;
}
case 3:{
struct i2c_board_info info = { };
f(c);
i2c_new_device(&info);
break;
}
case 4:{
struct i2c_board_info info = { };
f(d);
i2c_new_device(&info);
break;
}
}
return 0;
}
$ cc -v
Using built-in specs.
COLLECT_GCC=cc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/loongarch64-unknown-linux-gnu/14.2.0/lto-wrapper
Target: loongarch64-unknown-linux-gnu
Configured with: ../configure --prefix=/usr LD=ld --enable-languages=c,c++ --enable-default-pie --enable-default-ssp --disable-multilib --with-build-config=bootstrap-lto --disable-fixincludes --with-system-zlib --enable-host-pie
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 14.2.0 (GCC)
$ cc t.c -S -Wframe-larger-than=1 -DNONORETURN -O2
t.c: In function 'em28xx_dvb_init':
t.c:50:1: warning: the frame size of 144 bytes is larger than 1 bytes [-Wframe-larger-than=]
50 | }
| ^
$ cc t.c -S -Wframe-larger-than=1 -O2
t.c: In function 'em28xx_dvb_init':
t.c:50:1: warning: the frame size of 512 bytes is larger than 1 bytes [-Wframe-larger-than=]
50 | }
| ^
And I'm puzzled why "unreachable instruction" is not a problem on x86?
--
Xi Ruoyao <xry111@...111.site>
School of Aerospace Science and Technology, Xidian University
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