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dslm4515 / Musl-LFS

Linux From Scratch using Musl as Libc
GNU General Public License v3.0
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Why are we compiling a minimal version of libssp at 007-Musl instead of just using GCC's? #74

Open takusuman opened 2 years ago

takusuman commented 2 years ago

Reference: https://git.alpinelinux.org/aports/tree/main/musl/APKBUILD#n53 https://github.com/dslm4515/Musl-LFS/blob/stable-9.00/doc/3-Chroot/007-Musl#L27-L30

dslm4515 commented 2 years ago

Good question... I am not sure why, to be honest

I just copied over patches and APKBUILD from Alpine Linux and didn't evaluate each one... just to get GCC to build and work under musl. I would think by now, GCC would build under musl without patches.

I admit I didn't investigate why a minimal libssp was build instead of just using GCC's. I haven't gotten around testing GCC's libssp over the minimal one.

dslm4515 commented 2 years ago

Looking at the APKBUILD for GCC for Alpine Linux, it doesnt say why:

# alpine musl provides libssp_nonshared.a, so we don't need libssp either

And APKBUILD for musl:

# provide minimal libssp_nonshared.a so we don't need libssp from gcc
dslm4515 commented 2 years ago

Perhaps this explains it?

gcc did not do the right thing instead it has a (broken) libssp implementation ... so gcc allows the libc to implement ssp, but then it requires the libc to provide the loccal symbol too which is not possible (in case of dynamic linking). ..and it is a gcc internal target specific optimization thing so it does not make sense to do this in the libc even if it is possible.

what glibc does: the libc.so visible to ld is a linker script that magically adds glibc's libssp_nonshared.a to the link command. (and they build gcc with disabled libssp) (of course this linker script can cause horrible pains and misery)

what musl does: implements the public api in libc.so, but requires the compiler to provide the local definition. So e.g. you can build gcc with libssp enabled which has libssp_nonshared.a or you can provide one yourself.. but gcc does not add -lssp_nonshared if it thinks the libc provides ssp, so that's why those patches are needed: they add -lssp_nonshared back. (providing this lib yourself is better since that avoids uselessly building and installing the rest of libssp which can cause trouble if somebody accidentally uses -lssp explicitly)

source

takusuman commented 2 years ago

Perhaps this explains it?

gcc did not do the right thing instead it has a (broken) libssp implementation ... so gcc allows the libc to implement ssp, but then it requires the libc to provide the loccal symbol too which is not possible (in case of dynamic linking). ..and it is a gcc internal target specific optimization thing so it does not make sense to do this in the libc even if it is possible.

what glibc does: the libc.so visible to ld is a linker script that magically adds glibc's libssp_nonshared.a to the link command. (and they build gcc with disabled libssp) (of course this linker script can cause horrible pains and misery)

what musl does: implements the public api in libc.so, but requires the compiler to provide the local definition. So e.g. you can build gcc with libssp enabled which has libssp_nonshared.a or you can provide one yourself.. but gcc does not add -lssp_nonshared if it thinks the libc provides ssp, so that's why those patches are needed: they add -lssp_nonshared back. (providing this lib yourself is better since that avoids uselessly building and installing the rest of libssp which can cause trouble if somebody accidentally uses -lssp explicitly)

source

I think this explains pretty well, thanks a lot.

dslm4515 commented 2 years ago

I do really appreciate the questions. Sometimes I forget about the little details when I first struggled to get this project working!

I was wondering too every time I build MLFS... lol, but always forgot to investigate!

takusuman commented 2 years ago

I do really appreciate the questions. Sometimes I forget about the little details when I first struggled to get this project working!

I was wondering too every time I build MLFS... lol, but always forgot to investigate!

I'm investigating MLFS since 2021 for building Copacabana Linux and, as a result, I've been also writing a lot of documentation. May it can be a source/reference for some questions about MLFS' building process in the future (currently I'm still writing about it and it's only in portuguese yet).

takusuman commented 2 years ago

I do really appreciate the questions. Sometimes I forget about the little details when I first struggled to get this project working! I was wondering too every time I build MLFS... lol, but always forgot to investigate!

I'm investigating MLFS since 2021 for building Copacabana Linux and, as a result, I've been also writing a lot of documentation. May it can be a source/reference for some questions about MLFS' building process in the future (currently I'm still writing about it and it's only in portuguese yet).

There's also a lot of research in other sites, such as books, articles etc.