Markos Chandras [off-list ref] writes:

Hi,

On Tue, Feb 24, 2015 at 01:17:33PM +0000, Måns Rullgård wrote:

quoted

This patch (well, the variant that made it into 4.0-rc1) breaks
MIPS_ABI_FP_DOUBLE (the gcc default) apps on MIPS32.

Thanks for the report.

quoted

quoted

+void mips_set_personality_fp(struct arch_elf_state *state)
+{
+	/*
+	 * This function is only ever called for O32 ELFs so we should
+	 * not be worried about N32/N64 binaries.
+	 */

-	case MIPS_ABI_FP_XX:
-	case MIPS_ABI_FP_ANY:
-		if (!config_enabled(CONFIG_MIPS_O32_FP64_SUPPORT))
-			set_thread_flag(TIF_32BIT_FPREGS);
-		else
-			clear_thread_flag(TIF_32BIT_FPREGS);
+	if (!config_enabled(CONFIG_MIPS_O32_FP64_SUPPORT))
+		return;

The problem is here.  In a 32-bit configuration, MIPS_O32_FP64_SUPPORT
is always disabled, so the FP mode doesn't get set.  Simply deleting
those two lines makes things work again, but that's probably not the
right fix.

I had the impression that the loader would have set the FP mode earlier on.
But that only may happen with the latest version of the tools.

Perhaps instead of dropping these two lines we need a similar check on the
arch_elf_pt_proc so we don't mess with the default FPI abi?

Having said that, dropping these two lines should be fine, it just means you
do a little bit of extra work when loading your ELF files to check for ABI
compatibility which shouldn't matter in your case.

There's another early return like this in arch_check_elf() which should
probably go as well, or everything will end up with the default mode.

-- 
Måns Rullgård
mans@mansr.com