[Qemu-devel] [PULL v2 5/7] linux-user: elf: Map empty PT_LOAD segments

[Laurent Vivier <laurent@vivier.eu>]

From: Giuseppe Musacchio <thatlemon@gmail.com>

Some PT_LOAD segments may be completely zeroed out and their p_filesize
is zero, in that case the loader should just allocate a page that's at
least p_memsz bytes large (plus eventual alignment padding).

Calling zero_bss does this job for us, all we have to do is make sure we
don't try to mmap a zero-length page.

Signed-off-by: Giuseppe Musacchio <thatlemon@gmail.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20190503122007.lkjsvztgt4ycovac@debian>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
---
 linux-user/elfload.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index d08fe2346683..ef42e02d8233 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -2366,11 +2366,19 @@ static void load_elf_image(const char *image_name, int image_fd,
             vaddr_ps = TARGET_ELF_PAGESTART(vaddr);
             vaddr_len = TARGET_ELF_PAGELENGTH(eppnt->p_filesz + vaddr_po);
 
-            error = target_mmap(vaddr_ps, vaddr_len,
-                                elf_prot, MAP_PRIVATE | MAP_FIXED,
-                                image_fd, eppnt->p_offset - vaddr_po);
-            if (error == -1) {
-                goto exit_perror;
+            /*
+             * Some segments may be completely empty without any backing file
+             * segment, in that case just let zero_bss allocate an empty buffer
+             * for it.
+             */
+            if (eppnt->p_filesz != 0) {
+                error = target_mmap(vaddr_ps, vaddr_len, elf_prot,
+                                    MAP_PRIVATE | MAP_FIXED,
+                                    image_fd, eppnt->p_offset - vaddr_po);
+
+                if (error == -1) {
+                    goto exit_perror;
+                }
             }
 
             vaddr_ef = vaddr + eppnt->p_filesz;
-- 
2.20.1