Re: [PATCH v2] elfload: use g_new/g_malloc and g_autofree

[Elena Afanasova]

Subject: [PATCH v2] elfload: use g_new/g_malloc and g_autofree

Signed-off-by: Elena Afanasova <eafanasova@gmail.com>
---
 bsd-user/elfload.c | 79 ++++++++--------------------------------------
 1 file changed, 14 insertions(+), 65 deletions(-)

diff --git a/bsd-user/elfload.c b/bsd-user/elfload.c
index 32378af7b2..bc4be4c874 100644
--- a/bsd-user/elfload.c
+++ b/bsd-user/elfload.c
@@ -838,7 +838,7 @@ static abi_ulong load_elf_interp(struct elfhdr * 
interp_elf_ex,
                                  int interpreter_fd,
                                  abi_ulong *interp_load_addr)
 {
-        struct elf_phdr *elf_phdata  =  NULL;
+        g_autofree struct elf_phdr *elf_phdata = NULL;
         struct elf_phdr *eppnt;
         abi_ulong load_addr = 0;
         int load_addr_set = 0;
@@ -867,18 +867,13 @@ static abi_ulong load_elf_interp(struct elfhdr * 
interp_elf_ex,
         if (sizeof(struct elf_phdr) * interp_elf_ex->e_phnum > 
TARGET_PAGE_SIZE)
             return ~(abi_ulong)0UL;
 
-        elf_phdata =  (struct elf_phdr *)
-                malloc(sizeof(struct elf_phdr) * interp_elf_ex->e_phnum);
-
-        if (!elf_phdata)
-          return ~((abi_ulong)0UL);
+        elf_phdata = g_new(struct elf_phdr, interp_elf_ex->e_phnum);
 
         /*
          * If the size of this structure has changed, then punt, since
          * we will be doing the wrong thing.
          */
         if (interp_elf_ex->e_phentsize != sizeof(struct elf_phdr)) {
-            free(elf_phdata);
             return ~((abi_ulong)0UL);
         }
 
@@ -891,7 +886,6 @@ static abi_ulong load_elf_interp(struct elfhdr * 
interp_elf_ex,
         if (retval < 0) {
                 perror("load_elf_interp");
                 exit(-1);
-                free (elf_phdata);
                 return retval;
         }
 #ifdef BSWAP_NEEDED
@@ -940,7 +934,6 @@ static abi_ulong load_elf_interp(struct elfhdr * 
interp_elf_ex,
             if (error == -1) {
               /* Real error */
               close(interpreter_fd);
-              free(elf_phdata);
               return ~((abi_ulong)0UL);
             }
 
@@ -983,7 +976,6 @@ static abi_ulong load_elf_interp(struct elfhdr * 
interp_elf_ex,
                         PROT_READ|PROT_WRITE|PROT_EXEC,
                         MAP_FIXED|MAP_PRIVATE|MAP_ANON, -1, 0);
         }
-        free(elf_phdata);
 
         *interp_load_addr = load_addr;
         return ((abi_ulong) interp_elf_ex->e_entry) + load_addr;
@@ -1036,9 +1028,10 @@ static void load_symbols(struct elfhdr *hdr, int fd)
 {
     unsigned int i, nsyms;
     struct elf_shdr sechdr, symtab, strtab;
-    char *strings;
-    struct syminfo *s;
-    struct elf_sym *syms, *new_syms;
+    g_autofree char *strings = NULL;
+    g_autofree struct syminfo *s = NULL;
+    g_autofree struct elf_sym *syms = NULL;
+    struct elf_sym *new_syms;
 
     lseek(fd, hdr->e_shoff, SEEK_SET);
     for (i = 0; i < hdr->e_shnum; i++) {
@@ -1064,24 +1057,12 @@ static void load_symbols(struct elfhdr *hdr, int fd)
 
  found:
     /* Now know where the strtab and symtab are.  Snarf them. */
-    s = malloc(sizeof(*s));
-    syms = malloc(symtab.sh_size);
-    if (!syms) {
-        free(s);
-        return;
-    }
-    s->disas_strtab = strings = malloc(strtab.sh_size);
-    if (!s->disas_strtab) {
-        free(s);
-        free(syms);
-        return;
-    }
+    s = g_new(struct syminfo, 1);
+    syms = g_malloc(symtab.sh_size);
+    s->disas_strtab = strings = g_new(char, strtab.sh_size);
 
     lseek(fd, symtab.sh_offset, SEEK_SET);
     if (read(fd, syms, symtab.sh_size) != symtab.sh_size) {
-        free(s);
-        free(syms);
-        free(strings);
         return;
     }
 
@@ -1113,22 +1094,13 @@ static void load_symbols(struct elfhdr *hdr, int fd)
         that we threw away.  Whether or not this has any effect on the
         memory allocation depends on the malloc implementation and how
         many symbols we managed to discard. */
-    new_syms = realloc(syms, nsyms * sizeof(*syms));
-    if (new_syms == NULL) {
-        free(s);
-        free(syms);
-        free(strings);
-        return;
-    }
+    new_syms = g_realloc(syms, nsyms * sizeof(*syms));
     syms = new_syms;
 
     qsort(syms, nsyms, sizeof(*syms), symcmp);
 
     lseek(fd, strtab.sh_offset, SEEK_SET);
     if (read(fd, strings, strtab.sh_size) != strtab.sh_size) {
-        free(s);
-        free(syms);
-        free(strings);
         return;
     }
     s->disas_num_syms = nsyms;
@@ -1156,10 +1128,10 @@ int load_elf_binary(struct linux_binprm * bprm, struct 
target_pt_regs * regs,
     unsigned char ibcs2_interpreter;
     int i;
     struct elf_phdr * elf_ppnt;
-    struct elf_phdr *elf_phdata;
+    g_autofree struct elf_phdr *elf_phdata = NULL;
     abi_ulong elf_bss, k, elf_brk;
     int retval;
-    char * elf_interpreter;
+    g_autofree char *elf_interpreter = NULL;
     abi_ulong elf_entry, interp_load_addr = 0;
     abi_ulong start_code, end_code, start_data, end_data;
     abi_ulong reloc_func_desc = 0;
@@ -1190,10 +1162,7 @@ int load_elf_binary(struct linux_binprm * bprm, struct 
target_pt_regs * regs,
     }
 
     /* Now read in all of the header information */
-    elf_phdata = (struct elf_phdr *)malloc(elf_ex.e_phentsize*elf_ex.e_phnum);
-    if (elf_phdata == NULL) {
-        return -ENOMEM;
-    }
+    elf_phdata = g_new(struct elf_phdr, elf_ex.e_phnum);
 
     retval = lseek(bprm->fd, elf_ex.e_phoff, SEEK_SET);
     if(retval > 0) {
@@ -1204,7 +1173,6 @@ int load_elf_binary(struct linux_binprm * bprm, struct 
target_pt_regs * regs,
     if (retval < 0) {
         perror("load_elf_binary");
         exit(-1);
-        free (elf_phdata);
         return -errno;
     }
 
@@ -1220,7 +1188,6 @@ int load_elf_binary(struct linux_binprm * bprm, struct 
target_pt_regs * regs,
     elf_brk = 0;
 
 
-    elf_interpreter = NULL;
     start_code = ~((abi_ulong)0UL);
     end_code = 0;
     start_data = 0;
@@ -1231,8 +1198,6 @@ int load_elf_binary(struct linux_binprm * bprm, struct 
target_pt_regs * regs,
         if (elf_ppnt->p_type == PT_INTERP) {
             if ( elf_interpreter != NULL )
             {
-                free (elf_phdata);
-                free(elf_interpreter);
                 close(bprm->fd);
                 return -EINVAL;
             }
@@ -1242,13 +1207,7 @@ int load_elf_binary(struct linux_binprm * bprm, struct 
target_pt_regs * regs,
              * is an a.out format binary
              */
 
-            elf_interpreter = (char *)malloc(elf_ppnt->p_filesz);
-
-            if (elf_interpreter == NULL) {
-                free (elf_phdata);
-                close(bprm->fd);
-                return -ENOMEM;
-            }
+            elf_interpreter = g_new(char, elf_ppnt->p_filesz);
 
             retval = lseek(bprm->fd, elf_ppnt->p_offset, SEEK_SET);
             if(retval >= 0) {
@@ -1298,8 +1257,6 @@ int load_elf_binary(struct linux_binprm * bprm, struct 
target_pt_regs * regs,
             if (retval < 0) {
                 perror("load_elf_binary3");
                 exit(-1);
-                free (elf_phdata);
-                free(elf_interpreter);
                 close(bprm->fd);
                 return retval;
             }
@@ -1323,8 +1280,6 @@ int load_elf_binary(struct linux_binprm * bprm, struct 
target_pt_regs * regs,
         }
 
         if (!interpreter_type) {
-            free(elf_interpreter);
-            free(elf_phdata);
             close(bprm->fd);
             return -ELIBBAD;
         }
@@ -1346,8 +1301,6 @@ int load_elf_binary(struct linux_binprm * bprm, struct 
target_pt_regs * regs,
             }
         }
         if (!bprm->p) {
-            free(elf_interpreter);
-            free (elf_phdata);
             close(bprm->fd);
             return -E2BIG;
         }
@@ -1486,18 +1439,14 @@ int load_elf_binary(struct linux_binprm * bprm, struct 
target_pt_regs * regs,
         reloc_func_desc = interp_load_addr;
 
         close(interpreter_fd);
-        free(elf_interpreter);
 
         if (elf_entry == ~((abi_ulong)0UL)) {
             printf("Unable to load interpreter\n");
-            free(elf_phdata);
             exit(-1);
             return 0;
         }
     }
 
-    free(elf_phdata);
-
     if (qemu_log_enabled())
         load_symbols(&elf_ex, bprm->fd);
 
-- 
2.25.1

On Fri, 2020-10-02 at 10:08 -0500, Eric Blake wrote:
> On 10/2/20 3:58 AM, Markus Armbruster wrote:
> 
> > > > > @@ -890,9 +886,8 @@ static abi_ulong load_elf_interp(struct
> > > > > elfhdr * interp_elf_ex,
> > > > >          }
> > > > >          if (retval < 0) {
> > > > >                  perror("load_elf_interp");
> > > > > +                g_free(elf_phdata);
> > > > >                  exit(-1);
> > > > > -                free (elf_phdata);
> > > > > -                return retval;
> > > > 
> > > > Deleting return looks wrong.
> > > 
> > > Why? There is an exit(-1) right in front of it, so this is dead
> > > code...
> > > well, maybe that should be done in a separate patch, or at least
> > > mentioned in the patch description, though.
> > 
> > You're right; I missed the exit(-1).
> > 
> > Following the unpleasant odour spread by exit(-1)...  Aha, the
> > function's behavior on error is inconsistent: sometimes it returns
> > zero,
> > sometimes it exits.
> 
> Eradicating exit(-1) (which is indistinguishable from exit(255), and
> generally not what you want, unless your program is designed to
> specifically invoke the immediate-exit semantics of xargs) is also a
> worthwhile cleanup project.  But I agree with the advice for separate
> patches for separate bugs.
> 
> > Since the problem is bigger than just one dead return, I recommend
> > leaving it to a separate patch, and keeping this one focused on
> > g_new().
> > 
> >