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df99da19c6
Building with GCC with -Warray-bounds enabled there are several warnings
in sstep.c along the lines of:
In function ‘do_byte_reverse’,
inlined from ‘do_vec_load’ at arch/powerpc/lib/sstep.c:691:3,
inlined from ‘emulate_loadstore’ at arch/powerpc/lib/sstep.c:3439:9:
arch/powerpc/lib/sstep.c:289:23: error: array subscript 2 is outside array bounds of ‘u8[16]’ {aka ‘unsigned char[16]’} [-Werror=array-bounds=]
289 | up[2] = byterev_8(up[1]);
| ~~~~~~^~~~~~~~~~~~~~~~~~
arch/powerpc/lib/sstep.c: In function ‘emulate_loadstore’:
arch/powerpc/lib/sstep.c:681:11: note: at offset 16 into object ‘u’ of size 16
681 | } u = {};
| ^
do_byte_reverse() supports a size up to 32 bytes, but in these cases the
caller is only passing a 16 byte buffer. In practice there is no bug,
do_vec_load() is only called from the LOAD_VMX case in emulate_loadstore().
That in turn is only reached when analyse_instr() recognises VMX ops,
and in all cases the size is no greater than 16:
$ git grep -w LOAD_VMX arch/powerpc/lib/sstep.c
arch/powerpc/lib/sstep.c: op->type = MKOP(LOAD_VMX, 0, 1);
arch/powerpc/lib/sstep.c: op->type = MKOP(LOAD_VMX, 0, 2);
arch/powerpc/lib/sstep.c: op->type = MKOP(LOAD_VMX, 0, 4);
arch/powerpc/lib/sstep.c: op->type = MKOP(LOAD_VMX, 0, 16);
Similarly for do_vec_store().
Although the warning is incorrect, the code would be safer if it clamped
the size from the caller to the known size of the buffer. Do that using
min_t().
Reported-by: Bagas Sanjaya <bagasdotme@gmail.com>
Closes: https://lore.kernel.org/linuxppc-dev/YpbUcPrm61RLIiZF@debian.me/
Reported-by: Jan-Benedict Glaw <jbglaw@lug-owl.de>
Closes: https://lore.kernel.org/linuxppc-dev/20221212215117.aa7255t7qd6yefk4@lug-owl.de/
Reported-by: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Closes: https://lore.kernel.org/linuxppc-dev/6a8bf78c-aedb-4d5a-b0aa-82a51a17b884@embeddedor.com/
Reviewed-by: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Build-tested-by: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20231120235436.1569255-1-mpe@ellerman.id.au
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.