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149 lines
5.3 KiB
149 lines
5.3 KiB
commit dcbc6b83eff5b9238170bdfed834ba934150895f
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Author: Florian Weimer <fweimer@redhat.com>
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Date: Thu May 28 10:20:56 2020 +0200
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elf: Do not read hwcaps from the vDSO in ld.so
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This was only ever used for the "nosegneg" flag. This approach for
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passing hardware capability information creates a subtle dependency
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between the kernel and userspace, and ld.so.cache contents. It seems
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inappropriate for toady, where people expect to be able to run
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system images which very different kernel versions.
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Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
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diff --git a/elf/dl-hwcaps.c b/elf/dl-hwcaps.c
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index ecf00b457760e517..ae2e4ca7fe91d407 100644
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--- a/elf/dl-hwcaps.c
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+++ b/elf/dl-hwcaps.c
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@@ -26,12 +26,6 @@
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#include <dl-procinfo.h>
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#include <dl-hwcaps.h>
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-#ifdef _DL_FIRST_PLATFORM
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-# define _DL_FIRST_EXTRA (_DL_FIRST_PLATFORM + _DL_PLATFORMS_COUNT)
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-#else
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-# define _DL_FIRST_EXTRA _DL_HWCAP_COUNT
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-#endif
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-
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/* Return an array of useful/necessary hardware capability names. */
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const struct r_strlenpair *
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_dl_important_hwcaps (const char *platform, size_t platform_len, size_t *sz,
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@@ -52,116 +46,12 @@ _dl_important_hwcaps (const char *platform, size_t platform_len, size_t *sz,
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if ((masked & (1ULL << n)) != 0)
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++cnt;
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-#ifdef NEED_DL_SYSINFO_DSO
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- /* The system-supplied DSO can contain a note of type 2, vendor "GNU".
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- This gives us a list of names to treat as fake hwcap bits. */
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-
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- const char *dsocaps = NULL;
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- size_t dsocapslen = 0;
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- if (GLRO(dl_sysinfo_map) != NULL)
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- {
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- const ElfW(Phdr) *const phdr = GLRO(dl_sysinfo_map)->l_phdr;
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- const ElfW(Word) phnum = GLRO(dl_sysinfo_map)->l_phnum;
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- for (uint_fast16_t i = 0; i < phnum; ++i)
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- if (phdr[i].p_type == PT_NOTE)
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- {
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- const ElfW(Addr) start = (phdr[i].p_vaddr
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- + GLRO(dl_sysinfo_map)->l_addr);
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- /* NB: Some PT_NOTE segment may have alignment value of 0
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- or 1. gABI specifies that PT_NOTE segments should be
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- aligned to 4 bytes in 32-bit objects and to 8 bytes in
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- 64-bit objects. As a Linux extension, we also support
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- 4 byte alignment in 64-bit objects. If p_align is less
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- than 4, we treate alignment as 4 bytes since some note
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- segments have 0 or 1 byte alignment. */
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- ElfW(Addr) align = phdr[i].p_align;
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- if (align < 4)
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- align = 4;
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- else if (align != 4 && align != 8)
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- continue;
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- /* The standard ELF note layout is exactly as the anonymous struct.
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- The next element is a variable length vendor name of length
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- VENDORLEN (with a real length rounded to ElfW(Word)), followed
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- by the data of length DATALEN (with a real length rounded to
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- ElfW(Word)). */
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- const struct
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- {
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- ElfW(Word) vendorlen;
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- ElfW(Word) datalen;
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- ElfW(Word) type;
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- } *note = (const void *) start;
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- while ((ElfW(Addr)) (note + 1) - start < phdr[i].p_memsz)
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- {
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- /* The layout of the type 2, vendor "GNU" note is as follows:
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- .long <Number of capabilities enabled by this note>
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- .long <Capabilities mask> (as mask >> _DL_FIRST_EXTRA).
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- .byte <The bit number for the next capability>
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- .asciz <The name of the capability>. */
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- if (note->type == NT_GNU_HWCAP
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- && note->vendorlen == sizeof "GNU"
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- && !memcmp ((note + 1), "GNU", sizeof "GNU")
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- && note->datalen > 2 * sizeof (ElfW(Word)) + 2)
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- {
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- const ElfW(Word) *p
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- = ((const void *) note
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- + ELF_NOTE_DESC_OFFSET (sizeof "GNU", align));
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- cnt += *p++;
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- ++p; /* Skip mask word. */
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- dsocaps = (const char *) p; /* Pseudo-string "<b>name" */
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- dsocapslen = note->datalen - sizeof *p * 2;
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- break;
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- }
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- note = ((const void *) note
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- + ELF_NOTE_NEXT_OFFSET (note->vendorlen,
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- note->datalen, align));
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- }
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- if (dsocaps != NULL)
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- break;
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- }
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- }
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-#endif
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-
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/* For TLS enabled builds always add 'tls'. */
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++cnt;
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/* Create temporary data structure to generate result table. */
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struct r_strlenpair temp[cnt];
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m = 0;
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-#ifdef NEED_DL_SYSINFO_DSO
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- if (dsocaps != NULL)
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- {
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- /* dsocaps points to the .asciz string, and -1 points to the mask
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- .long just before the string. */
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- const ElfW(Word) mask = ((const ElfW(Word) *) dsocaps)[-1];
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- GLRO(dl_hwcap) |= (uint64_t) mask << _DL_FIRST_EXTRA;
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- /* Note that we add the dsocaps to the set already chosen by the
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- LD_HWCAP_MASK environment variable (or default HWCAP_IMPORTANT).
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- So there is no way to request ignoring an OS-supplied dsocap
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- string and bit like you can ignore an OS-supplied HWCAP bit. */
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- hwcap_mask |= (uint64_t) mask << _DL_FIRST_EXTRA;
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-#if HAVE_TUNABLES
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- TUNABLE_SET (glibc, cpu, hwcap_mask, uint64_t, hwcap_mask);
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-#else
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- GLRO(dl_hwcap_mask) = hwcap_mask;
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-#endif
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- size_t len;
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- for (const char *p = dsocaps; p < dsocaps + dsocapslen; p += len + 1)
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- {
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- uint_fast8_t bit = *p++;
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- len = strlen (p);
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-
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- /* Skip entries that are not enabled in the mask word. */
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- if (__glibc_likely (mask & ((ElfW(Word)) 1 << bit)))
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- {
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- temp[m].str = p;
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- temp[m].len = len;
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- ++m;
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- }
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- else
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- --cnt;
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- }
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- }
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-#endif
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for (n = 0; masked != 0; ++n)
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if ((masked & (1ULL << n)) != 0)
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{
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