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From: Rongwei Wang <rongwei.wang@linux.alibaba.com>
To: libc-alpha@sourceware.org, hjl.tools@gmail.com,
	fweimer@redhat.com, adhemerval.zanella@linaro.org
Cc: xuyu@linux.alibaba.com, gavin.dg@linux.alibaba.com
Subject: [PATCH v6 1/2] elf: Properly align PT_LOAD segments [BZ #28676]
Date: Mon, 13 Dec 2021 10:51:02 +0800	[thread overview]
Message-ID: <20211213025103.48472-2-rongwei.wang@linux.alibaba.com> (raw)
In-Reply-To: <20211213025103.48472-1-rongwei.wang@linux.alibaba.com>

When PT_LOAD segment alignment > the page size, allocate
enough space to ensure that the segment can be properly
aligned.

And this change helps code segments use huge pages become
simple and available.

This fixes [BZ #28676].

Signed-off-by: Xu Yu <xuyu@linux.alibaba.com>
Signed-off-by: Rongwei Wang <rongwei.wang@linux.alibaba.com>
---
 elf/dl-load.c         |  2 ++
 elf/dl-load.h         |  3 ++-
 elf/dl-map-segments.h | 50 +++++++++++++++++++++++++++++++++++++++----
 3 files changed, 50 insertions(+), 5 deletions(-)

diff --git a/elf/dl-load.c b/elf/dl-load.c
index bf8957e73c..721593135e 100644
--- a/elf/dl-load.c
+++ b/elf/dl-load.c
@@ -1,5 +1,6 @@
 /* Map in a shared object's segments from the file.
    Copyright (C) 1995-2021 Free Software Foundation, Inc.
+   Copyright The GNU Toolchain Authors.
    This file is part of the GNU C Library.
 
    The GNU C Library is free software; you can redistribute it and/or
@@ -1150,6 +1151,7 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
 	  c->mapend = ALIGN_UP (ph->p_vaddr + ph->p_filesz, GLRO(dl_pagesize));
 	  c->dataend = ph->p_vaddr + ph->p_filesz;
 	  c->allocend = ph->p_vaddr + ph->p_memsz;
+	  c->mapalign = ph->p_align;
 	  c->mapoff = ALIGN_DOWN (ph->p_offset, GLRO(dl_pagesize));
 
 	  /* Determine whether there is a gap between the last segment
diff --git a/elf/dl-load.h b/elf/dl-load.h
index e329d49a81..e6dabcb336 100644
--- a/elf/dl-load.h
+++ b/elf/dl-load.h
@@ -1,5 +1,6 @@
 /* Map in a shared object's segments from the file.
    Copyright (C) 1995-2021 Free Software Foundation, Inc.
+   Copyright The GNU Toolchain Authors.
    This file is part of the GNU C Library.
 
    The GNU C Library is free software; you can redistribute it and/or
@@ -74,7 +75,7 @@ ELF_PREFERRED_ADDRESS_DATA;
    Its details have been expanded out and converted.  */
 struct loadcmd
 {
-  ElfW(Addr) mapstart, mapend, dataend, allocend;
+  ElfW(Addr) mapstart, mapend, dataend, allocend, mapalign;
   ElfW(Off) mapoff;
   int prot;                             /* PROT_* bits.  */
 };
diff --git a/elf/dl-map-segments.h b/elf/dl-map-segments.h
index f9fb110ee3..70a4c40695 100644
--- a/elf/dl-map-segments.h
+++ b/elf/dl-map-segments.h
@@ -1,5 +1,6 @@
 /* Map in a shared object's segments.  Generic version.
    Copyright (C) 1995-2021 Free Software Foundation, Inc.
+   Copyright The GNU Toolchain Authors.
    This file is part of the GNU C Library.
 
    The GNU C Library is free software; you can redistribute it and/or
@@ -18,6 +19,50 @@
 
 #include <dl-load.h>
 
+/* Map a segment and align it properly.  */
+
+static __always_inline ElfW(Addr)
+_dl_map_segment (const struct loadcmd *c, ElfW(Addr) mappref,
+		 const size_t maplength, int fd)
+{
+  if (__glibc_likely (c->mapalign <= GLRO(dl_pagesize)))
+    return (ElfW(Addr)) __mmap ((void *) mappref, maplength, c->prot,
+				MAP_COPY|MAP_FILE, fd, c->mapoff);
+
+  /* If the segment alignment > the page size, allocate enough space to
+     ensure that the segment can be properly aligned.  */
+  ElfW(Addr) maplen = (maplength >= c->mapalign
+		       ? (maplength + c->mapalign)
+		       : (2 * c->mapalign));
+  ElfW(Addr) map_start = (ElfW(Addr)) __mmap ((void *) mappref, maplen,
+					      PROT_NONE,
+					      MAP_ANONYMOUS|MAP_PRIVATE,
+					      -1, 0);
+  if (__glibc_unlikely ((void *) map_start == MAP_FAILED))
+    return map_start;
+
+  ElfW(Addr) map_start_aligned = ALIGN_UP (map_start, c->mapalign);
+  map_start_aligned = (ElfW(Addr)) __mmap ((void *) map_start_aligned,
+					   maplength, c->prot,
+					   MAP_COPY|MAP_FILE|MAP_FIXED,
+					   fd, c->mapoff);
+  if (__glibc_unlikely ((void *) map_start_aligned == MAP_FAILED))
+    __munmap ((void *) map_start, maplen);
+  else
+    {
+      /* Unmap the unused regions.  */
+      ElfW(Addr) delta = map_start_aligned - map_start;
+      if (delta)
+	__munmap ((void *) map_start, delta);
+      ElfW(Addr) map_end = map_start_aligned + maplength;
+      delta = map_start + maplen - map_end;
+      if (delta)
+	__munmap ((void *) map_end, delta);
+    }
+
+  return map_start_aligned;
+}
+
 /* 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
@@ -53,10 +98,7 @@ _dl_map_segments (struct link_map *l, int fd,
            - 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);
+      l->l_map_start = _dl_map_segment (c, mappref, maplength, fd);
       if (__glibc_unlikely ((void *) l->l_map_start == MAP_FAILED))
         return DL_MAP_SEGMENTS_ERROR_MAP_SEGMENT;
 
-- 
2.27.0


  reply	other threads:[~2021-12-13  2:51 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-04  4:58 [PATCH RFC 0/1] make ld.so map .text LOAD ssegments and aligned by p_align Rongwei Wang
2021-12-04  4:58 ` [PATCH RFC 1/1] elf: align the mapping address of LOAD segments with p_align Rongwei Wang
2021-12-04 18:10   ` Florian Weimer
2021-12-06  2:47     ` Rongwei Wang
2021-12-06 14:48   ` H.J. Lu
2021-12-08  2:14     ` Rongwei Wang
2021-12-08  2:33       ` H.J. Lu
2021-12-08  3:04         ` Rongwei Wang
2021-12-08 23:52           ` H.J. Lu
2021-12-09  1:43             ` Rongwei Wang
2021-12-10 12:39 ` [PATCH v5 0/2] fix p_align on PT_LOAD segment in DSO isn't honored Rongwei Wang
2021-12-10 12:39   ` [PATCH v5 1/2] elf: Properly align PT_LOAD segments Rongwei Wang
2021-12-10 15:43     ` H.J. Lu
2021-12-10 15:45       ` Florian Weimer
2021-12-10 18:54         ` H.J. Lu
2021-12-10 18:57           ` H.J. Lu
2021-12-10 12:39   ` [PATCH v5 2/2] Add a testcase to check alignment of PT_LOAD segment Rongwei Wang
2021-12-10 13:48     ` Adhemerval Zanella
2021-12-10 15:41       ` H.J. Lu
2021-12-10 18:56         ` H.J. Lu
2021-12-10 20:05           ` Adhemerval Zanella
2021-12-10 20:24             ` H.J. Lu
2021-12-10 21:34               ` Adhemerval Zanella
2021-12-10 13:13   ` [PATCH v5 0/2] fix p_align on PT_LOAD segment in DSO isn't honored H.J. Lu
2021-12-10 13:58     ` Rongwei Wang
2021-12-13  2:51 ` [PATCH v6 " Rongwei Wang
2021-12-13  2:51   ` Rongwei Wang [this message]
2021-12-13 11:05     ` [PATCH v6 1/2] elf: Properly align PT_LOAD segments [BZ #28676] Szabolcs Nagy
2021-12-13 11:17       ` Florian Weimer
2021-12-13 11:35         ` Szabolcs Nagy
2021-12-13 11:59           ` Florian Weimer
2021-12-13 13:20             ` H.J. Lu
2021-12-13 13:26               ` Florian Weimer
2021-12-13 13:34                 ` H.J. Lu
2021-12-13 11:46     ` Andreas Schwab
2021-12-13 11:52       ` Szabolcs Nagy
2021-12-13 14:51         ` Rongwei Wang
2021-12-13 17:37           ` Szabolcs Nagy
2021-12-13 17:50             ` Florian Weimer
2021-12-13  2:51   ` [PATCH v6 2/2] Add a testcase to check alignment of PT_LOAD segment Rongwei Wang
2021-12-14  2:03   ` [PATCH v6 0/2] fix p_align on PT_LOAD segment in DSO isn't honored Fangrui Song
2021-12-14  3:56     ` H.J. Lu

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