From 8512287a8165592466cb9cb347ba94892e9c56a5 Mon Sep 17 00:00:00 2001 From: Nathan Lynch Date: Wed, 25 Mar 2015 19:14:22 +0100 Subject: ARM: 8330/1: add VDSO user-space code Place VDSO-related user-space code in arch/arm/kernel/vdso/. It is almost completely written in C with some assembly helpers to load the data page address, sample the counter, and fall back to system calls when necessary. The VDSO can service gettimeofday and clock_gettime when CONFIG_ARM_ARCH_TIMER is enabled and the architected timer is present (and correctly configured). It reads the CP15-based virtual counter to compute high-resolution timestamps. Of particular note is that a post-processing step ("vdsomunge") is necessary to produce a shared object which is architecturally allowed to be used by both soft- and hard-float EABI programs. The 2012 edition of the ARM ABI defines Tag_ABI_VFP_args = 3 "Code is compatible with both the base and VFP variants; the user did not permit non-variadic functions to pass FP parameters/results." Unfortunately current toolchains do not support this tag, which is ideally what we would use. The best available option is to ensure that both EF_ARM_ABI_FLOAT_SOFT and EF_ARM_ABI_FLOAT_HARD are unset in the ELF header's e_flags, indicating that the shared object is "old" and should be accepted for backward compatibility's sake. While binutils < 2.24 appear to produce a vdso.so with both flags clear, 2.24 always sets EF_ARM_ABI_FLOAT_SOFT, with no way to inhibit this behavior. So we have to fix things up with a custom post-processing step. In fact, the VDSO code in glibc does much less validation (including checking these flags) than the code for handling conventional file-backed shared libraries, so this is a bit moot unless glibc's VDSO code becomes more strict. Signed-off-by: Nathan Lynch Signed-off-by: Russell King --- arch/arm/vdso/.gitignore | 1 + 1 file changed, 1 insertion(+) create mode 100644 arch/arm/vdso/.gitignore (limited to 'arch/arm/vdso/.gitignore') diff --git a/arch/arm/vdso/.gitignore b/arch/arm/vdso/.gitignore new file mode 100644 index 000000000000..f8b69d84238e --- /dev/null +++ b/arch/arm/vdso/.gitignore @@ -0,0 +1 @@ +vdso.lds -- cgit v1.2.3