* [PATCH v2 0/1] fix p_align on PT_LOAD segment in DSO isn't honored @ 2021-12-09 5:49 Rongwei Wang 2021-12-09 5:49 ` [PATCH v2 1/1] elf: align the mapping address of LOAD segments with p_align Rongwei Wang 0 siblings, 1 reply; 4+ messages in thread From: Rongwei Wang @ 2021-12-09 5:49 UTC (permalink / raw) To: libc-alpha, hjl.tools, fweimer; +Cc: xuyu, gavin.dg Hi This patch mainly to fix a reported bug: "p_align on PT_LOAD segment in DSO isn't honored" https://sourceware.org/bugzilla/show_bug.cgi?id=28676 A testcase had been builded by H.J.Lu: https://sourceware.org/bugzilla/attachment.cgi?id=13838 And in Patch 1/1, I also show a simple testcase which modified from H.J.Lu. And a similar bug in ELF binary was also reported: https://bugzilla.kernel.org/show_bug.cgi?id=215275 A related fix patch could been found: https://lore.kernel.org/linux-mm/20211009092658.59665-4-rongwei.wang@linux.alibaba.com/ Originally, we send this patch for introducing .text hugepages, was not aware of it's bug. And now, I am not sure whether kernel maintainer will regards it as a bug. But it deserved try again. Thanks. Changelog: RFC/v1 -> v2 - Patch "elf: align the mapping address of LOAD segments with p_align" fix coding format and add testcase in commit. RFC link: https://patchwork.sourceware.org/project/glibc/patch/20211204045848.71105-2-rongwei.wang@linux.alibaba.com/ Rongwei Wang (1): elf: align the mapping address of LOAD segments with p_align elf/dl-load.c | 1 + elf/dl-map-segments.h | 63 +++++++++++++++++++++++++++++++++++++++---- include/link.h | 3 +++ 3 files changed, 62 insertions(+), 5 deletions(-) -- 2.27.0 ^ permalink raw reply [flat|nested] 4+ messages in thread
* [PATCH v2 1/1] elf: align the mapping address of LOAD segments with p_align 2021-12-09 5:49 [PATCH v2 0/1] fix p_align on PT_LOAD segment in DSO isn't honored Rongwei Wang @ 2021-12-09 5:49 ` Rongwei Wang 0 siblings, 0 replies; 4+ messages in thread From: Rongwei Wang @ 2021-12-09 5:49 UTC (permalink / raw) To: libc-alpha, hjl.tools, fweimer; +Cc: xuyu, gavin.dg Now, ld.so always map the LOAD segments and aligned by base page size (e.g. 4k in x86 or 4k, 16k and 64k in arm64). This is a bug, and had been reported: https://sourceware.org/bugzilla/show_bug.cgi?id=28676 This patch mainly to fix it. In this patch, ld.so can align the mapping address of the first LOAD segment with p_align when p_align is greater than the current base page size. A testcase: main.c: extern void dso_test(void); int main(void) { dso_test(); getchar(); return 0; } load.c, used to generate libload.so: int foo __attribute__((aligned(0x200000))) = 1; void dso_test(void) { printf("dso test\n"); printf("foo: %p\n", &foo); } The steps: $ gcc -O2 -fPIC -c -o load.o load.c $ gcc -shared -Wl,-z,max-page-size=0x200000 -o libload.so load.o $ gcc -no-pie -Wl,-z,max-page-size=0x200000 -O2 -o dso main.c libload.so -Wl,-R,. Before fixing: $ ./dso dso test foo: 0xffff88ae2000 After fixed: $ ./dso dso test foo: 0xffff9e000000 And this fix can help code segments use huge pages become simple and available. Signed-off-by: Xu Yu <xuyu@linux.alibaba.com> Signed-off-by: Rongwei Wang <rongwei.wang@linux.alibaba.com> --- elf/dl-load.c | 1 + elf/dl-map-segments.h | 63 +++++++++++++++++++++++++++++++++++++++---- include/link.h | 3 +++ 3 files changed, 62 insertions(+), 5 deletions(-) diff --git a/elf/dl-load.c b/elf/dl-load.c index e39980fb19..136cfe2fa8 100644 --- a/elf/dl-load.c +++ b/elf/dl-load.c @@ -1154,6 +1154,7 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd, c->dataend = ph->p_vaddr + ph->p_filesz; c->allocend = ph->p_vaddr + ph->p_memsz; c->mapoff = ALIGN_DOWN (ph->p_offset, GLRO(dl_pagesize)); + l->l_load_align = ph->p_align; /* Determine whether there is a gap between the last segment and this one. */ diff --git a/elf/dl-map-segments.h b/elf/dl-map-segments.h index ac9f09ab4c..fad98eb984 100644 --- a/elf/dl-map-segments.h +++ b/elf/dl-map-segments.h @@ -18,6 +18,48 @@ #include <dl-load.h> +static __always_inline void * +_dl_map_segments_align (const struct loadcmd *c, + ElfW(Addr) mappref, int fd, size_t alignment, + const size_t maplength) +{ + unsigned long map_start, map_start_align, map_end; + unsigned long maplen = (maplength >= alignment) ? + (maplength + alignment) : (2 * alignment); + + /* Allocate enough space to ensure that address aligned by + p_align is included. */ + map_start = (ElfW(Addr)) __mmap ((void *) mappref, maplen, + PROT_NONE, + MAP_ANONYMOUS | MAP_PRIVATE, + -1, 0); + if (__glibc_unlikely ((void *) map_start == MAP_FAILED)) + { + /* If mapping a aligned address failed, then ... */ + map_start = (ElfW(Addr)) __mmap ((void *) mappref, maplength, + c->prot, + MAP_COPY|MAP_FILE, + fd, c->mapoff); + + return (void *) map_start; + } + map_start_align = ALIGN_UP(map_start, alignment); + map_end = map_start_align + maplength; + + /* Remember which part of the address space this object uses. */ + map_start_align = (ElfW(Addr)) __mmap ((void *) map_start_align, maplength, + c->prot, + MAP_COPY|MAP_FILE|MAP_FIXED, + fd, c->mapoff); + if (__glibc_unlikely ((void *) map_start_align == MAP_FAILED)) + return MAP_FAILED; + if (map_start_align > map_start) + __munmap((void *)map_start, map_start_align - map_start); + __munmap((void *)map_end, map_start + maplen - map_end); + + return (void *) map_start_align; +} + /* This implementation assumes (as does the corresponding implementation of _dl_unmap_segments, in dl-unmap-segments.h) that shared objects are always laid out with all segments contiguous (or with gaps @@ -52,11 +94,22 @@ _dl_map_segments (struct link_map *l, int fd, c->mapstart & GLRO(dl_use_load_bias)) - MAP_BASE_ADDR (l)); - /* Remember which part of the address space this object uses. */ - l->l_map_start = (ElfW(Addr)) __mmap ((void *) mappref, maplength, - c->prot, - MAP_COPY|MAP_FILE, - fd, c->mapoff); + /* During mapping, align the mapping address of the LOAD segments + according to own p_align. This helps OS map its code segment to + huge pages. */ + if (l->l_load_align > GLRO(dl_pagesize)) + { + l->l_map_start = (ElfW(Addr)) _dl_map_segments_align (c, mappref, + fd, l->l_load_align, maplength); + } + else + { + /* Remember which part of the address space this object uses. */ + l->l_map_start = (ElfW(Addr)) __mmap ((void *) mappref, maplength, + c->prot, + MAP_COPY|MAP_FILE, + fd, c->mapoff); + } if (__glibc_unlikely ((void *) l->l_map_start == MAP_FAILED)) return DL_MAP_SEGMENTS_ERROR_MAP_SEGMENT; diff --git a/include/link.h b/include/link.h index aea268439c..fc6ce29fab 100644 --- a/include/link.h +++ b/include/link.h @@ -298,6 +298,9 @@ struct link_map /* Thread-local storage related info. */ + /* Alignment requirement of the LOAD block. */ + size_t l_load_align; + /* Start of the initialization image. */ void *l_tls_initimage; /* Size of the initialization image. */ -- 2.27.0 ^ permalink raw reply [flat|nested] 4+ messages in thread
* [PATCH v2 0/1] fix p_align on PT_LOAD segment in DSO isn't honored @ 2021-12-09 5:57 Rongwei Wang 2021-12-09 6:36 ` Rongwei Wang 0 siblings, 1 reply; 4+ messages in thread From: Rongwei Wang @ 2021-12-09 5:57 UTC (permalink / raw) To: libc-alpha, hjl.tools, fweimer; +Cc: xuyu, gavin.dg Hi This patch mainly to fix a reported bug: "p_align on PT_LOAD segment in DSO isn't honored" https://sourceware.org/bugzilla/show_bug.cgi?id=28676 A testcase had been builded by H.J.Lu: https://sourceware.org/bugzilla/attachment.cgi?id=13838 And in Patch 1/1, I also show a simple testcase which modified from H.J.Lu. And a similar bug in ELF binary was also reported: https://bugzilla.kernel.org/show_bug.cgi?id=215275 A related fix patch could been found: https://lore.kernel.org/linux-mm/20211009092658.59665-4-rongwei.wang@linux.alibaba.com/ Originally, we send this patch for introducing .text hugepages, was not aware of it's bug. And now, I am not sure whether kernel maintainer will regards it as a bug. But it deserved try again. Thanks. Changelog: RFC/v1 -> v2 - Patch "elf: align the mapping address of LOAD segments with p_align" fix coding format and add testcase in commit. RFC link: https://patchwork.sourceware.org/project/glibc/patch/20211204045848.71105-2-rongwei.wang@linux.alibaba.com/ Rongwei Wang (1): elf: align the mapping address of LOAD segments with p_align elf/dl-load.c | 1 + elf/dl-map-segments.h | 63 +++++++++++++++++++++++++++++++++++++++---- include/link.h | 3 +++ 3 files changed, 62 insertions(+), 5 deletions(-) -- 2.27.0 ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v2 0/1] fix p_align on PT_LOAD segment in DSO isn't honored 2021-12-09 5:57 [PATCH v2 0/1] fix p_align on PT_LOAD segment in DSO isn't honored Rongwei Wang @ 2021-12-09 6:36 ` Rongwei Wang 0 siblings, 0 replies; 4+ messages in thread From: Rongwei Wang @ 2021-12-09 6:36 UTC (permalink / raw) To: 20211204045848.71105-1-rongwei.wang, libc-alpha, hjl.tools, fweimer Cc: xuyu, gavin.dg Sorry, I took a mistake, sent this patch twice. The patch twice sent were completely same. Just read one patch is OK. Sorry for this mistake again. On 12/9/21 1:57 PM, Rongwei Wang via Libc-alpha wrote: > Hi > > This patch mainly to fix a reported bug: > > "p_align on PT_LOAD segment in DSO isn't honored" > https://sourceware.org/bugzilla/show_bug.cgi?id=28676 > > A testcase had been builded by H.J.Lu: > https://sourceware.org/bugzilla/attachment.cgi?id=13838 > > And in Patch 1/1, I also show a simple testcase which > modified from H.J.Lu. > > And a similar bug in ELF binary was also reported: > https://bugzilla.kernel.org/show_bug.cgi?id=215275 > > A related fix patch could been found: > https://lore.kernel.org/linux-mm/20211009092658.59665-4-rongwei.wang@linux.alibaba.com/ > Originally, we send this patch for introducing .text > hugepages, was not aware of it's bug. And now, I am > not sure whether kernel maintainer will regards it as > a bug. But it deserved try again. > > Thanks. > > Changelog: > > RFC/v1 -> v2 > > - Patch "elf: align the mapping address of LOAD segments with p_align" > fix coding format and add testcase in commit. > > RFC link: > https://patchwork.sourceware.org/project/glibc/patch/20211204045848.71105-2-rongwei.wang@linux.alibaba.com/ > > Rongwei Wang (1): > elf: align the mapping address of LOAD segments with p_align > > elf/dl-load.c | 1 + > elf/dl-map-segments.h | 63 +++++++++++++++++++++++++++++++++++++++---- > include/link.h | 3 +++ > 3 files changed, 62 insertions(+), 5 deletions(-) > ^ permalink raw reply [flat|nested] 4+ messages in thread
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