Segher, any response to my findings below about whether we should try and share header files with GLIBC?
Peter On 6/27/17 1:06 PM, Peter Bergner wrote: > On 6/27/17 11:07 AM, Segher Boessenkool wrote: >> Not use an installed header, that's not what I'm asking. Share the >> source file, i.e., just copy it over from the glibc source tree (it >> should probably hold the master copy). Fewer typos, cannot forget to >> update some entry, etc. > > So the glibc file is: > > sysdeps/powerpc/bits/hwcap.h > > which contains only the #define PPC_FEATURE[2]_* definitions. > The GCC file is: > > gcc/config/rs6000/ppc-auxv.h > > and contains the same #define's as hwcap.h above, plus the additional > #defines's: > > /* The PLATFORM value stored in the TCB is offset by _DL_FIRST_PLATFORM. */ > #define _DL_FIRST_PLATFORM 32 > > /* AT_PLATFORM bits. These must match the values defined in GLIBC. */ > #define PPC_PLATFORM_POWER4 0 > #define PPC_PLATFORM_PPC970 1 > #define PPC_PLATFORM_POWER5 2 > ... > > which match values in glibc's sysdeps/powerpc/dl-procinfo.h, but that > file contains a lot more than just the defines that we (GCC) doesn't > want or need. > > ppc-auxv.h also contains the following helper macros that calculate the > fixed offsets to the TCB slots that glibc initializes, but glibc has > access to the structs that the slows live in, so they don't need these > helper macros and hence don't have them: > > /* Thread Control Block (TCB) offsets of the AT_PLATFORM, AT_HWCAP and > AT_HWCAP2 values. These must match the values defined in GLIBC. */ > #define TCB_PLATFORM_OFFSET ((TARGET_64BIT) ? -28764 : -28724) > #define TCB_HWCAP_BASE_OFFSET ((TARGET_64BIT) ? -28776 : -28736) > #define TCB_HWCAP1_OFFSET \ > ((BYTES_BIG_ENDIAN) ? TCB_HWCAP_BASE_OFFSET : TCB_HWCAP_BASE_OFFSET+4) > #define TCB_HWCAP2_OFFSET \ > ((BYTES_BIG_ENDIAN) ? TCB_HWCAP_BASE_OFFSET+4 : TCB_HWCAP_BASE_OFFSET) > #define TCB_HWCAP_OFFSET(ID) \ > (((ID) == 0) ? TCB_HWCAP1_OFFSET : TCB_HWCAP2_OFFSET) > > These are only used in rs6000.c, so I could move them there. > > So given the above, how do we want to handle this? If we were to copy a > header file(s) over from glibc, are we able to modify it in the process? > Ie, to remove the parts we don't need like hwcap.h's use of: > > #if !defined(_SYS_AUXV_H) && !defined(_SYSDEPS_SYSDEP_H) > # error "Never include <bits/hwcap.h> directly; use <sys/auxv.h> instead." > #endif > > which would trigger for our use of it. And also to remove unneeded code from > dl-procinfo.h, since we only want the #defines. > > Peter > >
