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Message-ID: <20240116204552.GV4163@brightrain.aerifal.cx>
Date: Tue, 16 Jan 2024 15:45:52 -0500
From: Rich Felker <dalias@...c.org>
To: Cody Wetzel <codyawetzel@...il.com>,
Natanael Copa <ncopa@...inelinux.org>, musl@...ts.openwall.com,
Markus Wichmann <nullplan@....net>
Subject: Re: Segmentation fault musl 1.2.4
On Tue, Jan 16, 2024 at 07:29:18PM +0100, Szabolcs Nagy wrote:
> * Cody Wetzel <codyawetzel@...il.com> [2024-01-16 09:21:05 -0600]:
> > Here is the output for the old
> > ....
> > >
> > > / # /tmp/ld-musl-armhf.so.1 /usr/bin/readelf -lW /tmp/ld-musl-armhf.so.1
> > >
> > > Elf file type is DYN (Shared object file)
> > > Entry point 0x359cd
> > > There are 6 program headers, starting at offset 52
> > >
> > > Program Headers:
> > > Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
> > > EXIDX 0x07acec 0x0007acec 0x0007acec 0x00008 0x00008 R 0x4
> > > LOAD 0x000000 0x00000000 0x00000000 0x7acf4 0x7acf4 R E 0x10000
> > > LOAD 0x07fd6c 0x0008fd6c 0x0008fd6c 0x0054a 0x02258 RW 0x10000
>
> this load segment is 64k aligned.
>
> > > DYNAMIC 0x07febc 0x0008febc 0x0008febc 0x000c0 0x000c0 RW 0x4
> > > GNU_STACK 0x000000 0x00000000 0x00000000 0x00000 0x00000 RW 0x10
> > > GNU_RELRO 0x07fd6c 0x0008fd6c 0x0008fd6c 0x00294 0x00294 R 0x1
> > >
> > > Section to Segment mapping:
> > > Segment Sections...
> > > 00 .ARM.exidx
> > > 01 .hash .gnu.hash .dynsym .dynstr .rel.dyn .rel.plt .plt .text
> > > .rodata .ARM.exidx
> > > 02 .data.rel.ro .dynamic .got .data .bss
> > > 03 .dynamic
> > > 04
> > > 05 .data.rel.ro .dynamic .got
> > >
> >
> > And the new...
> >
> > / # /tmp/ld-musl-armhf.so.1 /usr/bin/readelf -lW /lib/ld-musl-armhf.so.1
> > >
> > > Elf file type is DYN (Shared object file)
> > > Entry point 0x362f1
> > > There are 6 program headers, starting at offset 52
> > >
> > > Program Headers:
> > > Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
> > > EXIDX 0x07b81c 0x0007b81c 0x0007b81c 0x00008 0x00008 R 0x4
> > > LOAD 0x000000 0x00000000 0x00000000 0x7b824 0x7b824 R E 0x1000
> > > LOAD 0x07bd74 0x0007cd74 0x0007cd74 0x0054a 0x0225c RW 0x1000
>
> this load segment is 4k aligned and offset vs addr is not congruent
> modulo 64k, or 32k, so won't work on systems with such page size.
>
> > > DYNAMIC 0x07bebc 0x0007cebc 0x0007cebc 0x000c0 0x000c0 RW 0x4
> > > GNU_STACK 0x000000 0x00000000 0x00000000 0x00000 0x00000 RW 0x10
> > > GNU_RELRO 0x07bd74 0x0007cd74 0x0007cd74 0x0028c 0x0028c R 0x1
> > >
> > > Section to Segment mapping:
> > > Segment Sections...
> > > 00 .ARM.exidx
> > > 01 .hash .gnu.hash .dynsym .dynstr .rel.dyn .rel.plt .plt .text
> > > .rodata .ARM.exidx
> > > 02 .data.rel.ro .dynamic .got .data .bss
> > > 03 .dynamic
> > > 04
> > > 05 .data.rel.ro .dynamic .got
> >
> >
> > I hope that helps.
>
> yes, this is a linking issue, not musl libc.
>
> alpine linux links binaries for 4k pagesize only.
>
> arm linkers were updated at some point to create binaries supporting
> up to 64k pagesize. i suspect some ppl ran into issues in practice
> and decided the larger binaries are not worth it, if they dont work
> reliably and forced 4k page size at link time.
>
> you have to raise an issue with alpine linux, if you think 32k
> oage size is useful and reliably supportable.
Are they using -Wl,-z,separate-code? That incurs a large
binary-size-on-disk penalty when supporting oversized pages, and IIRC
something was done to make the linker default to not supporting
oversized pages when that's used. It might be the reason, if arm
linking is normally expected to use a larger max pagesize.
Rich
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