Reported by Leah Neukirchen.
patch by Pascal Cuoq.
in arm rtabi these __aeabi_* functions have special abi (they are only allowed to clobber r0,r1,r2,r3,ip,lr,cpsr), so they cannot be simple wrappers around normal string functions (which may clobber other registers), the safest solution is to write them in asm, a minimalistic implementation works because these are not supposed to be emitted by compilers or used in general.
the thumb incompatibilities in the asm are probably only minor and should be fixable, but for now just use the C version.
the two/three/four byte memmem specializations are not prepared to handle haystacks shorter than the needle; they unconditionally read at least up to the needle length and subtract from the haystack length. if the haystack is shorter, the remaining haystack length underflows and produces an unbounded search which will eventually either crash or find a spurious match. the top-level memmem function attempted to avoid this case already by checking for haystack shorter than needle, but it failed to re-check after using memchr to remove the maximal prefix not containing the first byte of the needle.
this is possible with the new build system that allows src/*/$(ARCH)/* files which do not shadow a file in the parent directory, and yields a more logical organization. eventually it will be possible to remove arch/*/src from the build system.
this depends on commit 9f5eb77992b42d484d69e879d24ef86466f20f21, which made it possible to use a .c file for arch-specific replacements, and on commit 2f853dd6b9a95d5b13ee8f9df762125e0588df5d, the out-of-tree build support, which made it so that src/*/$(ARCH)/* 'replacement' files get used even if they don't match the base name of a .c file in the parent directory.
the idea of the three-instruction sequence being removed was to be able to return to thumb code when used on armv4t+ from a thumb caller, but also to be able to run on armv4 without the bx instruction available (in which case the low bit of lr would always be 0). however, without compiler support for generating such a sequence from C code, which does not exist and which there is unlikely to be interest in implementing, there is little point in having it in the asm, and it would likely be easier to add pre-armv4t support via enhanced linker handling of R_ARM_V4BX than at the compiler level. removing this code simplifies adding support for building libc in thumb2-only form (for cortex-m).
contrary to commit 9367fe926196f407705bb07cd29c6e40eb1774dd, all relevant gas versions actually do support .syntax unified.
this interface is non-standardized and is a GNU invention, and as such, our implementation should match the behavior of the GNU function. one peculiarity the old implementation got wrong was the handling of all-zero digit sequences: they are supposed to compare greater than digit sequences of which they are a proper prefix, as in 009 < 00. in addition, high bytes were treated with char signedness rather than as unsigned. this was wrong regardless of what the GNU function does since the resulting order relation varied by arch. the new strverscmp implementation makes explicit the cases where the order differs from what strcmp would produce, of which there are only two.