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Date: Tue, 30 Jan 2024 11:43:38 +0100
From: Szabolcs Nagy <nsz@...t70.net>
To: Rich Felker <dalias@...c.org>
Cc: 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
* Rich Felker <dalias@...c.org> [2024-01-16 15:45:52 -0500]:
> 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.
i looked at this now, turns out they just changed the
pagesize back to 4k (i missed this change):
https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=1a26a53a0dee39106ba58fcb15496c5f13074652
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