Re: [PATCH] Revert "elf: Relax MIPS' elf_check_arch() to accept EM_NANOMIPS too"

[Philippe Mathieu-Daudé]

On 11/1/21 22:40, Vince Del Vecchio wrote:
> Philippe said:
> 
>> So far QEMU only support the MIPS o32 / n32 / n64 ABIs. The p32 ABI is not 
>> implemented, therefore we can not run any nanoMIPS binary.
> 
> We use it internally to run nanoMIPS binaries every day.  I had thought 
> everything relevant was completed and upstreamed, but perhaps there is a gap 
> somewhere.  Let us investigate a little and get back to you.

I could wait few days until QEMU hard freeze and queue this patch as a
bug fix, but I doubt there is much you can do in that time frame, since
tomorrow is the soft freeze deadline.

Here I am simply changing the code to reject p32 binaries to avoid
users to waste their time trying to run a nanoMIPS binary. I am not
removing any of the nanoMIPS emulation code.

> Were you trying to run a bare metal executable or was it linux?

While I tested both toolchains (bare metal and musl/linux), here I am
only referring to the musl/linux one, since it is related to user-mode
emulation (files under linux-user/ directory).

The system emulation part is left unchanged (you can still boot a
nanoMIPS kernel if you select the proper CPU type).

> -----Original Message-----
> From: Qemu-devel 
> <qemu-devel-bounces+vince.delvecchio=mediatek.com@nongnu.org> On Behalf Of 
> Philippe Mathieu-Daudé
> Sent: Monday, November 1, 2021 7:48 AM
> To: qemu-devel@nongnu.org
> Cc: Aleksandar Rikalo <aleksandar.rikalo@syrmia.com>; Richard Henderson 
> <richard.henderson@linaro.org>; Laurent Vivier <laurent@vivier.eu>; Philippe 
> Mathieu-Daudé <f4bug@amsat.org>; Petar Jovanovic 
> <petar.jovanovic@syrmia.com>; Aurelien Jarno <aurelien@aurel32.net>
> Subject: [PATCH] Revert "elf: Relax MIPS' elf_check_arch() to accept 
> EM_NANOMIPS too"
> 
> Per the "P32 Porting Guide" (rev 1.2) [1], chapter 2:
> 
>   p32 ABI Overview
>   ----------------
> 
>   The Application Binary Interface, or ABI, is the set of rules
>   that all binaries must follow in order to run on a nanoMIPS
>   system. This includes, for example, object file format,
>   instruction set, data layout, subroutine calling convention,
>   and system call numbers. The ABI is one part of the mechanism
>   that maintains binary compatibility across all nanoMIPS platforms.
> 
>   p32 improves on o32 to provide an ABI that is efficient in both
>   code density and performance. p32 is required for the nanoMIPS
>   architecture.
> 
> So far QEMU only support the MIPS o32 / n32 / n64 ABIs. The p32 ABI is not 
> implemented, therefore we can not run any nanoMIPS binary.
> 
> Revert commit f72541f3a59 ("elf: Relax MIPS' elf_check_arch() to accept 
> EM_NANOMIPS too").
> 
> See also the "ELF ABI Supplement" [2].
> 
> [1] 
> http://codescape.mips.com/components/toolchain/nanomips/2019.03-01/docs/MIPS_nanoMIPS_p32_ABI_Porting_Guide_01_02_DN00184.pdf
> [2] 
> http://codescape.mips.com/components/toolchain/nanomips/2019.03-01/docs/MIPS_nanoMIPS_ABI_supplement_01_03_DN00179.pdf
> 
> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> ---
>  linux-user/elfload.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/linux-user/elfload.c b/linux-user/elfload.c index 
> f9b82616920..5da8c02d082 100644
> --- a/linux-user/elfload.c
> +++ b/linux-user/elfload.c
> @@ -925,8 +925,6 @@ static void elf_core_copy_regs(target_elf_gregset_t 
> *regs, const CPUPPCState *en  #endif
>  #define ELF_ARCH    EM_MIPS
>  
> -#define elf_check_arch(x) ((x) == EM_MIPS || (x) == EM_NANOMIPS)
> -
>  #ifdef TARGET_ABI_MIPSN32
>  #define elf_check_abi(x) ((x) & EF_MIPS_ABI2)  #else
> --
> 2.31.1