c++ abi

c++ abi

[Szabolcs Nagy]

[-- Attachment #1: Type: text/plain, Size: 531 bytes --]

for each type T i defined a function

 void x_T(T *x, size (*)[sizeof(T)], align (*)[alignof(T)]){}

(with some 'size' and 'align' struct types for readability)

so the mangled symbols in the c++ compiled object have the
abi info for each T that can be compared glibc vs musl

 nm abi.o |sed -n 's/^[[:xdigit:]]* T //p' |c++filt

unfortunately i only have the old musl cross compilers
(musl 1.1.2) and for glibc only gcc-4.4 cross compilers
(which only have __alignof__ instead of alignof) but some
of the findings may be relevant

[-- Attachment #2: arm.abi.diff --]
[-- Type: text/x-diff, Size: 1817 bytes --]

--- arm.glibc.abi	2014-09-09 02:34:28.618375521 +0200
+++ arm.musl.abi	2014-09-09 02:34:29.726381013 +0200
@@ -54 +54 @@
-x___jmp_buf(int*, size (*) [256], align (*) [8])
+x___jmp_buf(unsigned long long*, size (*) [256], align (*) [8])
@@ -60,2 +60,2 @@
-x_fexcept_t(unsigned int, size (*) [4], align (*) [4])
-x_gregset_t(unsigned long*, size (*) [72], align (*) [4])
+x_fexcept_t(unsigned long, size (*) [4], align (*) [4])
+x_gregset_t(int*, size (*) [72], align (*) [4])
@@ -82 +82 @@
-x_siginfo_t(siginfo, size (*) [128], align (*) [4])
+x_siginfo_t(siginfo_t, size (*) [128], align (*) [4])
@@ -115 +115 @@
-x_crypt_data(crypt_data, size (*) [131228], align (*) [4])
+x_crypt_data(crypt_data, size (*) [260], align (*) [4])
@@ -161 +161 @@
-x_sched_param(sched_param, size (*) [4], align (*) [4])
+x_sched_param(sched_param, size (*) [28], align (*) [4])
@@ -184 +184 @@
-x_ether_header(ether_header, size (*) [14], align (*) [1])
+x_ether_header(ether_header, size (*) [14], align (*) [2])
@@ -237 +237 @@
-x_pthread_cond_t(pthread_cond_t, size (*) [48], align (*) [8])
+x_pthread_cond_t(pthread_cond_t, size (*) [48], align (*) [4])
@@ -273 +273 @@
-x_CODE(_code, size (*) [8], align (*) [4])
+x_CODE(CODE, size (*) [8], align (*) [4])
@@ -331 +331 @@
-x_ethhdr(ethhdr, size (*) [14], align (*) [1])
+x_ethhdr(ethhdr, size (*) [14], align (*) [2])
@@ -358 +358 @@
-x_rusage(rusage, size (*) [72], align (*) [4])
+x_rusage(rusage, size (*) [136], align (*) [4])
@@ -377 +377 @@
-x_fd_mask(long, size (*) [4], align (*) [4])
+x_fd_mask(unsigned long, size (*) [4], align (*) [4])
@@ -419 +419 @@
-x_sysinfo(sysinfo, size (*) [64], align (*) [4])
+x_sysinfo(sysinfo, size (*) [312], align (*) [4])
@@ -421 +421 @@
-x_tftphdr(tftphdr, size (*) [5], align (*) [1])
+x_tftphdr(tftphdr, size (*) [6], align (*) [2])

[-- Attachment #3: i386.abi.diff --]
[-- Type: text/x-diff, Size: 1686 bytes --]

--- i386.glibc.abi	2014-09-09 01:49:04.876869217 +0200
+++ i386.musl.abi	2014-09-09 01:49:05.912874355 +0200
@@ -54 +54 @@
-x___jmp_buf(int*, size (*) [24], align (*) [4])
+x___jmp_buf(unsigned long*, size (*) [24], align (*) [4])
@@ -82 +82 @@
-x_siginfo_t(siginfo, size (*) [128], align (*) [4])
+x_siginfo_t(siginfo_t, size (*) [128], align (*) [4])
@@ -115 +115 @@
-x_crypt_data(crypt_data, size (*) [131228], align (*) [4])
+x_crypt_data(crypt_data, size (*) [260], align (*) [4])
@@ -120 +120 @@
-x_fpregset_t(_libc_fpstate*, size (*) [4], align (*) [4])
+x_fpregset_t(_fpstate*, size (*) [4], align (*) [4])
@@ -129 +129 @@
-x_ntptimeval(ntptimeval, size (*) [36], align (*) [4])
+x_ntptimeval(ntptimeval, size (*) [16], align (*) [4])
@@ -162 +162 @@
-x_sched_param(sched_param, size (*) [4], align (*) [4])
+x_sched_param(sched_param, size (*) [28], align (*) [4])
@@ -185 +185 @@
-x_ether_header(ether_header, size (*) [14], align (*) [1])
+x_ether_header(ether_header, size (*) [14], align (*) [2])
@@ -278 +278 @@
-x_CODE(_code, size (*) [8], align (*) [4])
+x_CODE(CODE, size (*) [8], align (*) [4])
@@ -336 +336 @@
-x_ethhdr(ethhdr, size (*) [14], align (*) [1])
+x_ethhdr(ethhdr, size (*) [14], align (*) [2])
@@ -363 +363 @@
-x_rusage(rusage, size (*) [72], align (*) [4])
+x_rusage(rusage, size (*) [136], align (*) [4])
@@ -382 +382 @@
-x_fd_mask(long, size (*) [4], align (*) [4])
+x_fd_mask(unsigned long, size (*) [4], align (*) [4])
@@ -424 +424 @@
-x_sysinfo(sysinfo, size (*) [64], align (*) [4])
+x_sysinfo(sysinfo, size (*) [312], align (*) [4])
@@ -426 +426 @@
-x_tftphdr(tftphdr, size (*) [5], align (*) [1])
+x_tftphdr(tftphdr, size (*) [6], align (*) [2])

[-- Attachment #4: mips.abi.diff --]
[-- Type: text/x-diff, Size: 2073 bytes --]

--- mips.glibc.abi	2014-09-09 02:39:58.052009103 +0200
+++ mips.musl.abi	2014-09-09 02:39:58.952013560 +0200
@@ -54 +54 @@
-x___jmp_buf(__jmp_buf_internal_tag*, size (*) [104], align (*) [8])
+x___jmp_buf(unsigned long long*, size (*) [104], align (*) [8])
@@ -81,2 +81,2 @@
-x_sigaction(sigaction, size (*) [144], align (*) [4])
-x_siginfo_t(siginfo, size (*) [128], align (*) [4])
+x_sigaction(sigaction, size (*) [140], align (*) [4])
+x_siginfo_t(siginfo_t, size (*) [128], align (*) [4])
@@ -115 +115 @@
-x_crypt_data(crypt_data, size (*) [131228], align (*) [4])
+x_crypt_data(crypt_data, size (*) [260], align (*) [4])
@@ -129 +129 @@
-x_prpsinfo_t(elf_prpsinfo, size (*) [128], align (*) [4])
+x_prpsinfo_t(elf_prpsinfo, size (*) [124], align (*) [4])
@@ -161 +161 @@
-x_sched_param(sched_param, size (*) [4], align (*) [4])
+x_sched_param(sched_param, size (*) [28], align (*) [4])
@@ -181 +181 @@
-x_elf_prpsinfo(elf_prpsinfo, size (*) [128], align (*) [4])
+x_elf_prpsinfo(elf_prpsinfo, size (*) [124], align (*) [4])
@@ -184 +184 @@
-x_ether_header(ether_header, size (*) [14], align (*) [1])
+x_ether_header(ether_header, size (*) [14], align (*) [2])
@@ -237 +237 @@
-x_pthread_cond_t(pthread_cond_t, size (*) [48], align (*) [8])
+x_pthread_cond_t(pthread_cond_t, size (*) [48], align (*) [4])
@@ -273 +273 @@
-x_CODE(_code, size (*) [8], align (*) [4])
+x_CODE(CODE, size (*) [8], align (*) [4])
@@ -331 +331 @@
-x_ethhdr(ethhdr, size (*) [14], align (*) [1])
+x_ethhdr(ethhdr, size (*) [14], align (*) [2])
@@ -357 +357 @@
-x_rusage(rusage, size (*) [72], align (*) [4])
+x_rusage(rusage, size (*) [136], align (*) [4])
@@ -376 +376 @@
-x_fd_mask(long, size (*) [4], align (*) [4])
+x_fd_mask(unsigned long, size (*) [4], align (*) [4])
@@ -418,3 +418,3 @@
-x_sysinfo(sysinfo, size (*) [64], align (*) [4])
-x_termios(termios, size (*) [52], align (*) [4])
-x_tftphdr(tftphdr, size (*) [5], align (*) [1])
+x_sysinfo(sysinfo, size (*) [312], align (*) [4])
+x_termios(termios, size (*) [60], align (*) [4])
+x_tftphdr(tftphdr, size (*) [6], align (*) [2])

[-- Attachment #5: powerpc.abi.diff --]
[-- Type: text/x-diff, Size: 2825 bytes --]

--- powerpc.glibc.abi	2014-09-09 02:36:16.450910234 +0200
+++ powerpc.musl.abi	2014-09-09 02:36:17.018913058 +0200
@@ -13 +13 @@
-x_ipc_perm(ipc_perm, size (*) [48], align (*) [8])
+x_ipc_perm(ipc_perm, size (*) [36], align (*) [4])
@@ -17 +17 @@
-x_msqid_ds(msqid_ds, size (*) [104], align (*) [8])
+x_msqid_ds(msqid_ds, size (*) [88], align (*) [4])
@@ -23 +23 @@
-x_semid_ds(semid_ds, size (*) [80], align (*) [8])
+x_semid_ds(semid_ds, size (*) [64], align (*) [4])
@@ -27 +27 @@
-x_shmid_ds(shmid_ds, size (*) [104], align (*) [8])
+x_shmid_ds(shmid_ds, size (*) [84], align (*) [4])
@@ -54 +54 @@
-x___jmp_buf(long*, size (*) [448], align (*) [16])
+x___jmp_buf(unsigned long long*, size (*) [448], align (*) [8])
@@ -82 +82 @@
-x_siginfo_t(siginfo, size (*) [128], align (*) [4])
+x_siginfo_t(siginfo_t, size (*) [128], align (*) [4])
@@ -115 +115 @@
-x_crypt_data(crypt_data, size (*) [131228], align (*) [4])
+x_crypt_data(crypt_data, size (*) [260], align (*) [4])
@@ -137 +137 @@
-x_sigjmp_buf(__jmp_buf_tag*, size (*) [592], align (*) [16])
+x_sigjmp_buf(__jmp_buf_tag*, size (*) [584], align (*) [8])
@@ -139 +139 @@
-x_ucontext_t(ucontext, size (*) [1184], align (*) [4])
+x_ucontext_t(ucontext, size (*) [1184], align (*) [16])
@@ -155 +155 @@
-x_long_double(__float128, size (*) [16], align (*) [16])
+x_long_double(long double, size (*) [8], align (*) [8])
@@ -161 +161 @@
-x_sched_param(sched_param, size (*) [4], align (*) [4])
+x_sched_param(sched_param, size (*) [28], align (*) [4])
@@ -184 +184 @@
-x_ether_header(ether_header, size (*) [14], align (*) [1])
+x_ether_header(ether_header, size (*) [14], align (*) [2])
@@ -215 +215 @@
-x___jmp_buf_tag(__jmp_buf_tag, size (*) [592], align (*) [16])
+x___jmp_buf_tag(__jmp_buf_tag, size (*) [584], align (*) [8])
@@ -237 +237 @@
-x_pthread_cond_t(pthread_cond_t, size (*) [48], align (*) [8])
+x_pthread_cond_t(pthread_cond_t, size (*) [48], align (*) [4])
@@ -273 +273 @@
-x_CODE(_code, size (*) [8], align (*) [4])
+x_CODE(CODE, size (*) [8], align (*) [4])
@@ -331 +331 @@
-x_ethhdr(ethhdr, size (*) [14], align (*) [1])
+x_ethhdr(ethhdr, size (*) [14], align (*) [2])
@@ -357 +357 @@
-x_rusage(rusage, size (*) [72], align (*) [4])
+x_rusage(rusage, size (*) [136], align (*) [4])
@@ -376 +376 @@
-x_fd_mask(long, size (*) [4], align (*) [4])
+x_fd_mask(unsigned long, size (*) [4], align (*) [4])
@@ -392 +392 @@
-x_jmp_buf(__jmp_buf_tag*, size (*) [592], align (*) [16])
+x_jmp_buf(__jmp_buf_tag*, size (*) [584], align (*) [8])
@@ -418,3 +418,3 @@
-x_sysinfo(sysinfo, size (*) [64], align (*) [4])
-x_termios(termios, size (*) [60], align (*) [4])
-x_tftphdr(tftphdr, size (*) [5], align (*) [1])
+x_sysinfo(sysinfo, size (*) [312], align (*) [4])
+x_termios(termios, size (*) [44], align (*) [4])
+x_tftphdr(tftphdr, size (*) [6], align (*) [2])

[-- Attachment #6: x86_64.abi.diff --]
[-- Type: text/x-diff, Size: 4029 bytes --]

--- x86_64.glibc.abi	2014-09-09 01:40:22.210277471 +0200
+++ x86_64.musl.abi	2014-09-09 01:41:04.618487657 +0200
@@ -22 +22 @@
-x_regoff_t(int, size (*) [4], align (*) [4])
+x_regoff_t(long, size (*) [8], align (*) [8])
@@ -38 +38 @@
-x_u_quad_t(unsigned long, size (*) [8], align (*) [8])
+x_u_quad_t(unsigned long long, size (*) [8], align (*) [8])
@@ -54 +54 @@
-x___jmp_buf(long*, size (*) [64], align (*) [8])
+x___jmp_buf(unsigned long*, size (*) [64], align (*) [8])
@@ -61 +61 @@
-x_gregset_t(long*, size (*) [184], align (*) [8])
+x_gregset_t(long long*, size (*) [184], align (*) [8])
@@ -82 +82 @@
-x_siginfo_t(siginfo, size (*) [128], align (*) [8])
+x_siginfo_t(siginfo_t, size (*) [128], align (*) [8])
@@ -115,2 +115,2 @@
-x_crypt_data(crypt_data, size (*) [131232], align (*) [8])
-x_elf_greg_t(unsigned long, size (*) [8], align (*) [8])
+x_crypt_data(crypt_data, size (*) [260], align (*) [4])
+x_elf_greg_t(unsigned long long, size (*) [8], align (*) [8])
@@ -120 +120 @@
-x_fpregset_t(_libc_fpstate*, size (*) [8], align (*) [8])
+x_fpregset_t(_fpstate*, size (*) [8], align (*) [8])
@@ -129 +129 @@
-x_ntptimeval(ntptimeval, size (*) [72], align (*) [8])
+x_ntptimeval(ntptimeval, size (*) [32], align (*) [8])
@@ -133 +133 @@
-x_regmatch_t(regmatch_t, size (*) [8], align (*) [4])
+x_regmatch_t(regmatch_t, size (*) [16], align (*) [8])
@@ -160 +160 @@
-x_prgregset_t(unsigned long*, size (*) [216], align (*) [8])
+x_prgregset_t(unsigned long long*, size (*) [216], align (*) [8])
@@ -162 +162 @@
-x_sched_param(sched_param, size (*) [4], align (*) [4])
+x_sched_param(sched_param, size (*) [48], align (*) [8])
@@ -185 +185 @@
-x_ether_header(ether_header, size (*) [14], align (*) [1])
+x_ether_header(ether_header, size (*) [14], align (*) [2])
@@ -190,2 +190,2 @@
-x_int_fast16_t(long, size (*) [8], align (*) [8])
-x_int_fast32_t(long, size (*) [8], align (*) [8])
+x_int_fast16_t(int, size (*) [4], align (*) [4])
+x_int_fast32_t(int, size (*) [4], align (*) [4])
@@ -217 +217 @@
-x_elf_gregset_t(unsigned long*, size (*) [216], align (*) [8])
+x_elf_gregset_t(unsigned long long*, size (*) [216], align (*) [8])
@@ -227,2 +227,2 @@
-x_uint_fast16_t(unsigned long, size (*) [8], align (*) [8])
-x_uint_fast32_t(unsigned long, size (*) [8], align (*) [8])
+x_uint_fast16_t(unsigned int, size (*) [4], align (*) [4])
+x_uint_fast32_t(unsigned int, size (*) [4], align (*) [4])
@@ -267 +267 @@
-x_pthread_rwlockattr_t(pthread_rwlockattr_t, size (*) [8], align (*) [8])
+x_pthread_rwlockattr_t(pthread_rwlockattr_t, size (*) [8], align (*) [4])
@@ -278 +278 @@
-x_CODE(_code, size (*) [16], align (*) [8])
+x_CODE(CODE, size (*) [16], align (*) [8])
@@ -317 +317 @@
-x_sem_t(sem_t, size (*) [32], align (*) [8])
+x_sem_t(sem_t, size (*) [32], align (*) [4])
@@ -326 +326 @@
-x_utmpx(utmpx, size (*) [384], align (*) [4])
+x_utmpx(utmpx, size (*) [400], align (*) [8])
@@ -336 +336 @@
-x_ethhdr(ethhdr, size (*) [14], align (*) [1])
+x_ethhdr(ethhdr, size (*) [14], align (*) [2])
@@ -342 +342 @@
-x_greg_t(long, size (*) [8], align (*) [8])
+x_greg_t(long long, size (*) [8], align (*) [8])
@@ -360,2 +360,2 @@
-x_quad_t(long, size (*) [8], align (*) [8])
-x_rlim_t(unsigned long, size (*) [8], align (*) [8])
+x_quad_t(long long, size (*) [8], align (*) [8])
+x_rlim_t(unsigned long long, size (*) [8], align (*) [8])
@@ -363 +363 @@
-x_rusage(rusage, size (*) [144], align (*) [8])
+x_rusage(rusage, size (*) [272], align (*) [8])
@@ -381,2 +381,2 @@
-x_cmsghdr(cmsghdr, size (*) [16], align (*) [8])
-x_fd_mask(long, size (*) [8], align (*) [8])
+x_cmsghdr(cmsghdr, size (*) [16], align (*) [4])
+x_fd_mask(unsigned long, size (*) [8], align (*) [8])
@@ -399 +399 @@
-x_lastlog(lastlog, size (*) [292], align (*) [4])
+x_lastlog(lastlog, size (*) [296], align (*) [8])
@@ -424 +424 @@
-x_sysinfo(sysinfo, size (*) [112], align (*) [8])
+x_sysinfo(sysinfo, size (*) [368], align (*) [8])
@@ -426 +426 @@
-x_tftphdr(tftphdr, size (*) [5], align (*) [1])
+x_tftphdr(tftphdr, size (*) [6], align (*) [2])

Re: c++ abi

[Szabolcs Nagy]

* Szabolcs Nagy <nsz@port70.net> [2014-09-09 03:04:06 +0200]:
> --- x86_64.glibc.abi	2014-09-09 01:40:22.210277471 +0200
> +++ x86_64.musl.abi	2014-09-09 01:41:04.618487657 +0200
...
> @@ -162 +162 @@
> -x_sched_param(sched_param, size (*) [4], align (*) [4])
> +x_sched_param(sched_param, size (*) [48], align (*) [8])
...
> @@ -267 +267 @@
> -x_pthread_rwlockattr_t(pthread_rwlockattr_t, size (*) [8], align (*) [8])
> +x_pthread_rwlockattr_t(pthread_rwlockattr_t, size (*) [8], align (*) [4])
...
> @@ -317 +317 @@
> -x_sem_t(sem_t, size (*) [32], align (*) [8])
> +x_sem_t(sem_t, size (*) [32], align (*) [4])
...
> @@ -360,2 +360,2 @@
> -x_quad_t(long, size (*) [8], align (*) [8])
> -x_rlim_t(unsigned long, size (*) [8], align (*) [8])
> +x_quad_t(long long, size (*) [8], align (*) [8])
> +x_rlim_t(unsigned long long, size (*) [8], align (*) [8])
> @@ -363 +363 @@
> -x_rusage(rusage, size (*) [144], align (*) [8])
> +x_rusage(rusage, size (*) [272], align (*) [8])
> @@ -381,2 +381,2 @@
> -x_cmsghdr(cmsghdr, size (*) [16], align (*) [8])
> -x_fd_mask(long, size (*) [8], align (*) [8])
> +x_cmsghdr(cmsghdr, size (*) [16], align (*) [4])
> +x_fd_mask(unsigned long, size (*) [8], align (*) [8])

cant the different size/alignment cause abi issues
when these types are used embedded into a struct?

and in case of rlim_t if it is used as an argument
to a c++ function

(the omitted diffs are known issues or not relavant to abi compat
i think)

Re: c++ abi

[Rich Felker]

On Tue, Sep 09, 2014 at 01:43:52PM +0200, Szabolcs Nagy wrote:
> * Szabolcs Nagy <nsz@port70.net> [2014-09-09 03:04:06 +0200]:
> > --- x86_64.glibc.abi	2014-09-09 01:40:22.210277471 +0200
> > +++ x86_64.musl.abi	2014-09-09 01:41:04.618487657 +0200
> ....
> > @@ -162 +162 @@
> > -x_sched_param(sched_param, size (*) [4], align (*) [4])
> > +x_sched_param(sched_param, size (*) [48], align (*) [8])
> ....
> > @@ -267 +267 @@
> > -x_pthread_rwlockattr_t(pthread_rwlockattr_t, size (*) [8], align (*) [8])
> > +x_pthread_rwlockattr_t(pthread_rwlockattr_t, size (*) [8], align (*) [4])
> ....
> > @@ -317 +317 @@
> > -x_sem_t(sem_t, size (*) [32], align (*) [8])
> > +x_sem_t(sem_t, size (*) [32], align (*) [4])

These alignment differences were unfortunate, but I think it would do
more harm than good trying to change now. They only affect ABI between
two TUs build against different libc headers that are using the above
types as part of the API between themselves. They do not affect the
ABI to libc; musl is happy to take glibc's over-aligned types.

> ....
> > @@ -360,2 +360,2 @@
> > -x_quad_t(long, size (*) [8], align (*) [8])
> > -x_rlim_t(unsigned long, size (*) [8], align (*) [8])
> > +x_quad_t(long long, size (*) [8], align (*) [8])
> > +x_rlim_t(unsigned long long, size (*) [8], align (*) [8])

quad_t is a nonstandard legacy type that never should have been used
to begin with, and I doubt it comes up in C++ at all. I'm indifferent
on fixing it.

rlim_t is probably unlikely to be used as an argument type in C++, but
I'd rather not break stuff using it.

> > @@ -363 +363 @@
> > -x_rusage(rusage, size (*) [144], align (*) [8])
> > +x_rusage(rusage, size (*) [272], align (*) [8])
> > @@ -381,2 +381,2 @@
> > -x_cmsghdr(cmsghdr, size (*) [16], align (*) [8])
> > -x_fd_mask(long, size (*) [8], align (*) [8])
> > +x_cmsghdr(cmsghdr, size (*) [16], align (*) [4])
> > +x_fd_mask(unsigned long, size (*) [8], align (*) [8])
> 
> cant the different size/alignment cause abi issues
> when these types are used embedded into a struct?

For cmsghdr, I don't think you would use it in a struct; it's normally
used as a string of multiple headers in an allocated buffer where a
pointer to the buffer is in the msghdr struct. But it might be nice if
we could fix this. It's even _possible_ that the missing alignment is
causing the macros that advance this struct to mismatch the kernel ABI
in some cases; this should be checked.

If that's determined not to be a problem, it's probably safest just to
leave it.

Rich