Re: [PATCH] Use CAS instead of atomic swap to implement spinlock

[Szabolcs Nagy <nsz@port70.net>]

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* Rich Felker <dalias@libc.org> [2015-04-19 02:01:32 -0400]:
> On Sun, Apr 19, 2015 at 08:50:18AM +0300, Alexander Monakov wrote:
> > On Sat, 18 Apr 2015, Rich Felker wrote:
> > > 
> > > while (*(volatile int *)s || a_cas(s, 0, 1)) a_spin();
> > 
> > I think so, Yes.  Is the cast required, or is it possible to change the
> > pthread_spinlock_t typedef to 'volatile int'?
> 
> For C++ ABI purposes, I think switching to volatile int would be a
> different type. :(
> 
> I wouldn't really be opposed to changing it for C and just having the
> ABI-compat type used when __cplusplus is defined. We already do that
> for pthread_t.
> 

btw pthread_spinlock_t is volatile int in glibc,
i didnt catch this abi diff earlier because it only matters when used
as a pointer

now changed my abi checks for all type T to do

 void x_T(T x, T* ptr, size(*y)[sizeof(T)], align(*z)[__alignof__(T)]){}

but i found no other case with qualifier differences
(updated x86_64 abi diffs are attached)

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--- abi.x86_64.glibc
+++ abi.x86_64.musl
@@ -2 +2 @@
-x_CODE(_code, _code*, size (*) [16], align (*) [8])
+x_CODE(CODE, CODE*, size (*) [16], align (*) [8])
@@ -69 +69 @@
-x___jmp_buf(long*, long (*) [8], size (*) [64], align (*) [8])
+x___jmp_buf(unsigned long*, unsigned long (*) [8], size (*) [64], align (*) [8])
@@ -97 +97 @@
-x_cmsghdr(cmsghdr, cmsghdr*, size (*) [16], align (*) [8])
+x_cmsghdr(cmsghdr, cmsghdr*, size (*) [16], align (*) [4])
@@ -100 +100 @@
-x_crypt_data(crypt_data, crypt_data*, size (*) [131232], align (*) [8])
+x_crypt_data(crypt_data, crypt_data*, size (*) [260], align (*) [4])
@@ -121,2 +121,2 @@
-x_ether_header(ether_header, ether_header*, size (*) [14], align (*) [1])
-x_ethhdr(ethhdr, ethhdr*, size (*) [14], align (*) [1])
+x_ether_header(ether_header, ether_header*, size (*) [14], align (*) [2])
+x_ethhdr(ethhdr, ethhdr*, size (*) [14], align (*) [2])
@@ -127 +127 @@
-x_fd_mask(long, long*, size (*) [8], align (*) [8])
+x_fd_mask(unsigned long, unsigned long*, size (*) [8], align (*) [8])
@@ -135 +135 @@
-x_fpregset_t(_libc_fpstate*, _libc_fpstate**, size (*) [8], align (*) [8])
+x_fpregset_t(_fpstate*, _fpstate**, size (*) [8], align (*) [8])
@@ -180,2 +180,2 @@
-x_int_fast16_t(long, long*, size (*) [8], align (*) [8])
-x_int_fast32_t(long, long*, size (*) [8], align (*) [8])
+x_int_fast16_t(int, int*, size (*) [4], align (*) [4])
+x_int_fast32_t(int, int*, size (*) [4], align (*) [4])
@@ -218 +218 @@
-x_lastlog(lastlog, lastlog*, size (*) [292], align (*) [4])
+x_lastlog(lastlog, lastlog*, size (*) [296], align (*) [8])
@@ -281 +281 @@
-x_ntptimeval(ntptimeval, ntptimeval*, size (*) [72], align (*) [8])
+x_ntptimeval(ntptimeval, ntptimeval*, size (*) [32], align (*) [8])
@@ -307,2 +307,2 @@
-x_pthread_rwlockattr_t(pthread_rwlockattr_t, pthread_rwlockattr_t*, size (*) [8], align (*) [8])
-x_pthread_spinlock_t(int, int volatile*, size (*) [4], align (*) [4])
+x_pthread_rwlockattr_t(pthread_rwlockattr_t, pthread_rwlockattr_t*, size (*) [8], align (*) [4])
+x_pthread_spinlock_t(int, int*, size (*) [4], align (*) [4])
@@ -312 +312 @@
-x_quad_t(long, long*, size (*) [8], align (*) [8])
+x_quad_t(long long, long long*, size (*) [8], align (*) [8])
@@ -317,2 +317,2 @@
-x_regmatch_t(regmatch_t, regmatch_t*, size (*) [8], align (*) [4])
-x_regoff_t(int, int*, size (*) [4], align (*) [4])
+x_regmatch_t(regmatch_t, regmatch_t*, size (*) [16], align (*) [8])
+x_regoff_t(long, long*, size (*) [8], align (*) [8])
@@ -321 +321 @@
-x_rlim_t(unsigned long, unsigned long*, size (*) [8], align (*) [8])
+x_rlim_t(unsigned long long, unsigned long long*, size (*) [8], align (*) [8])
@@ -327 +327 @@
-x_rusage(rusage, rusage*, size (*) [144], align (*) [8])
+x_rusage(rusage, rusage*, size (*) [272], align (*) [8])
@@ -329,2 +329,2 @@
-x_sched_param(sched_param, sched_param*, size (*) [4], align (*) [4])
-x_sem_t(sem_t, sem_t*, size (*) [32], align (*) [8])
+x_sched_param(sched_param, sched_param*, size (*) [48], align (*) [8])
+x_sem_t(sem_t, sem_t*, size (*) [32], align (*) [4])
@@ -383 +383 @@
-x_sysinfo(sysinfo, sysinfo*, size (*) [112], align (*) [8])
+x_sysinfo(sysinfo, sysinfo*, size (*) [368], align (*) [8])
@@ -385 +385 @@
-x_tcp_info(tcp_info, tcp_info*, size (*) [104], align (*) [4])
+x_tcp_info(tcp_info, tcp_info*, size (*) [120], align (*) [8])
@@ -389 +389 @@
-x_tftphdr(tftphdr, tftphdr*, size (*) [5], align (*) [1])
+x_tftphdr(tftphdr, tftphdr*, size (*) [6], align (*) [2])
@@ -407 +407 @@
-x_u_quad_t(unsigned long, unsigned long*, size (*) [8], align (*) [8])
+x_u_quad_t(unsigned long long, unsigned long long*, size (*) [8], align (*) [8])
@@ -418,2 +418,2 @@
-x_uint_fast16_t(unsigned long, unsigned long*, size (*) [8], align (*) [8])
-x_uint_fast32_t(unsigned long, unsigned long*, size (*) [8], align (*) [8])
+x_uint_fast16_t(unsigned int, unsigned int*, size (*) [4], align (*) [4])
+x_uint_fast32_t(unsigned int, unsigned int*, size (*) [4], align (*) [4])
@@ -435 +435 @@
-x_utmpx(utmpx, utmpx*, size (*) [384], align (*) [4])
+x_utmpx(utmpx, utmpx*, size (*) [400], align (*) [8])