[OpenWrt-Devel] [PATCH] build: always use -minterlink-mips16 if USE_MIPS16

[Felix Fietkau]

On 2020-05-25 02:19, Eneas U de Queiroz wrote:
> Individual packages may turn off MIPS16 ISA individually with
> PKG_USE_MIPS16.  However, they may link to a library compiled with
> MIPS16.  In such cases, the -minterlink-mips16 is needed to ensure there
> are no direct jumps to code compiled with a different ISA.
> 
> Instead of adding -minterlink-mips16 only when PKG_USE_MIPS16 is on, add
> it when global USE_MIPS16 is on.
> 
> Signed-off-by: Eneas U de Queiroz <cotequeiroz at gmail.com>
> ---
> Tested by compiling all packages in base, packages, routing and
> telephony feeds for mips_74kc, with MIPS16 enabled.
> 
> This was discovered while working on lxc fixes 
> (https://github.com/openwrt/packages/pull/12241), where compilation with
> mips16 would fail because of '-fstack-check=specific not implemented for
> MIPS16', and it would fail with PKG_USE_MIPS16=0 because of jumping to a
> different ISA mode:
> 
> lxc-4.0.2/src/lxc/caps.c:24:(.text+0xa4): unsupported jump between ISA
> modes; consider recompiling with interlinking enabled
> 
> In theory this could happen in more places, so set interlinking on
> whenever MIPS16 is turned on globally.
I think there needs be a way to opt-out of this behavior.
The -minterlink-mips16 flag affects the performance and code size of
generated code, so libraries that disable MIPS16 for performance reasons
and don't depend on other MIPS16 enabled libraries should not be
compiled with this flag.

- Felix

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