Re: copy lfs build to older CPU

On Fri, 2025-09-26 at 15:54 +0200, Thomas Seeling wrote:
> Hallo,
> > dmesg should show exactly which file contains the offending instruction.
> > Like:
> > 
> > [10066.276138] traps: a.out[100368] trap invalid opcode ip:7f0720a5f100 sp:7ffdcdaafd58 error:0 in t.so[1100,7f0720a5f000+1000]
> > 
> > And which exact files have you replaced?
> 
> I followed the instructions on the libffi and gmp packages, then used 
> "make DESTDIR=" to catch the files, transferred exactly the freshly 
> compiled files to the target and rebooted to make sure the new files are 
> there and not some cached old.
> 
> Still got the error below. dmesg showed nothing.

Try "sudo sysctl debug.exception-trace=1" before running the crashing
program.

> Compiling the first few files went through, and it choked here:

> 
> make[1]: Entering directory '/sources/ethtool-5.0'
>    CC       sff-common.o
> sff-common.c: In function "convert_mw_to_dbm":
> sff-common.c:29:9: internal compiler error: Illegal instruction
>     29 |         return (10. * log10(mw / 1000.)) + 30.;
>        |         ^~~~~~

This seems the first place where GCC invokes GMP (as it needs to
calculate the correctly rounded value of some FP operations using MPFR).
Thus I still either think GMP is not replaced correctly, or the book
instruction for building a microarchitecture-independent GMP is
incorrect.

Can you attach a build log of GMP and the exact command you use to
replace GMP?


-- 
Xi Ruoyao <[email protected]>

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