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Re: [PATCH][MIPS] Add linker emulation for N64 ABI with forced 32-bit symbols
- From: Richard Sandiford <rdsandiford at googlemail dot com>
- To: Maxim Kuvyrkov <maxim at codesourcery dot com>
- Cc: <binutils at sourceware dot org>, Eric Christopher <echristo at apple dot com>
- Date: Thu, 15 Nov 2012 22:08:12 +0000
- Subject: Re: [PATCH][MIPS] Add linker emulation for N64 ABI with forced 32-bit symbols
- References: <1A059C97-D083-4E17-A444-659452ABCCDB@codesourcery.com>
Maxim Kuvyrkov <email@example.com> writes:
> This patch fixes linking of applications compiled with -mabi=64 -msym32.
> The -msym32 GCC options forces MIPS backend to emit 32-bit symbols even
> when compiling for 64-bit ABI, which is most useful for building
> applications with PLTs to call shared library functions (PLTs are
> currently supported only for 32-bit symbols for MIPS). Certain
> applications get a significant performance edge from using PLTs, and
> such applications should be compiled with "-mabi=64 -mplt -msym32".
> Compiling with the above options works just fine until linker tries to
> put the .text section above 32-bit address space at
> TEXT_START_ADDR="0x120000000". This patch sets TEXT_START_ADDR to
> 0x10000000 (which is same as for N32 ABI) when compiling with -msym32
> GCC option.
> I will post the corresponding GCC patch that tells the linker to use new
> emulations shortly.
> Tested by building complete MIPS64 toolchain (including glibc) with -msym32.
> OK to apply?
Huh. I'm very much against the original change to the n64 TEXT_START_ADDR.
See this previous discussion on the topic:
The justification for changing TEXT_START_ADDR from a 32-bit value to a
larger value was that it would show users if their code was non-portable,
because anything that assumed 32-bit addresses would now fault. But that
seems to me like the tools lecturing to the user. As I said in that thread,
I think users who want to smoke out such portability problems (by making
sure that the lower 4GB aren't mapped) should be the ones who need to do
I think we should simply revert to a 32-bit TEXT_START_ADDR for all
n64 emulations. This time I'm even in a position to approve it :-)
That has the advantage that no GCC patches are needed. Users who
want this functionality can just upgrade their binutils.