xen/livepatch: Clean up arch relocation handling

* Reduce symbol scope and initalisation as much as possible
 * Annotate a fallthrough case in arm64
 * Fix switch statement style in arm32

No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Tested-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> [x86 and arm32]

xen/arch/arm/arm32/livepatch.c

@@ -224,21 +224,21 @@ int arch_livepatch_perform(struct livepatch_elf *elf,
                            const struct livepatch_elf_sec *rela,
                            bool use_rela)
 {
-    const Elf_RelA *r_a;
-    const Elf_Rel *r;
-    unsigned int symndx, i;
-    uint32_t val;
-    void *dest;
+    unsigned int i;
     int rc = 0;
 
     for ( i = 0; i < (rela->sec->sh_size / rela->sec->sh_entsize); i++ )
     {
+        unsigned int symndx;
+        uint32_t val;
+        void *dest;
         unsigned char type;
-        s32 addend = 0;
+        s32 addend;
 
         if ( use_rela )
         {
-            r_a = rela->data + i * rela->sec->sh_entsize;
+            const Elf_RelA *r_a = rela->data + i * rela->sec->sh_entsize;
+
             symndx = ELF32_R_SYM(r_a->r_info);
             type = ELF32_R_TYPE(r_a->r_info);
             dest = base->load_addr + r_a->r_offset; /* P */
@@ -246,10 +246,12 @@ int arch_livepatch_perform(struct livepatch_elf *elf,
         }
         else
         {
-            r = rela->data + i * rela->sec->sh_entsize;
+            const Elf_Rel *r = rela->data + i * rela->sec->sh_entsize;
+
             symndx = ELF32_R_SYM(r->r_info);
             type = ELF32_R_TYPE(r->r_info);
             dest = base->load_addr + r->r_offset; /* P */
+            addend = get_addend(type, dest);
         }
 
         if ( symndx > elf->nsym )
@@ -259,13 +261,11 @@ int arch_livepatch_perform(struct livepatch_elf *elf,
             return -EINVAL;
         }
 
-        if ( !use_rela )
-            addend = get_addend(type, dest);
-
         val = elf->sym[symndx].sym->st_value; /* S */
 
         rc = perform_rel(type, dest, val, addend);
-        switch ( rc ) {
+        switch ( rc )
+        {
         case -EOVERFLOW:
             dprintk(XENLOG_ERR, LIVEPATCH "%s: Overflow in relocation %u in %s for %s!\n",
                     elf->name, i, rela->name, base->name);
@@ -275,9 +275,6 @@ int arch_livepatch_perform(struct livepatch_elf *elf,
             dprintk(XENLOG_ERR, LIVEPATCH "%s: Unhandled relocation #%x\n",
                     elf->name, type);
             break;
-
-        default:
-            break;
         }
 
         if ( rc )

xen/arch/arm/arm64/livepatch.c

@@ -241,19 +241,16 @@ int arch_livepatch_perform_rela(struct livepatch_elf *elf,
                                 const struct livepatch_elf_sec *base,
                                 const struct livepatch_elf_sec *rela)
 {
-    const Elf_RelA *r;
-    unsigned int symndx, i;
-    uint64_t val;
-    void *dest;
-    bool_t overflow_check;
+    unsigned int i;
 
     for ( i = 0; i < (rela->sec->sh_size / rela->sec->sh_entsize); i++ )
     {
+        const Elf_RelA *r = rela->data + i * rela->sec->sh_entsize;
+        unsigned int symndx = ELF64_R_SYM(r->r_info);
+        void *dest = base->load_addr + r->r_offset; /* P */
+        bool overflow_check = true;
         int ovf = 0;
-
-        r = rela->data + i * rela->sec->sh_entsize;
-
-        symndx = ELF64_R_SYM(r->r_info);
+        uint64_t val;
 
         if ( symndx > elf->nsym )
         {
@@ -262,11 +259,8 @@ int arch_livepatch_perform_rela(struct livepatch_elf *elf,
             return -EINVAL;
         }
 
-        dest = base->load_addr + r->r_offset; /* P */
         val = elf->sym[symndx].sym->st_value +  r->r_addend; /* S+A */
 
-        overflow_check = true;
-
         /* ARM64 operations at minimum are always 32-bit. */
         if ( r->r_offset >= base->sec->sh_size ||
             (r->r_offset + sizeof(uint32_t)) > base->sec->sh_size )
@@ -403,6 +397,7 @@ int arch_livepatch_perform_rela(struct livepatch_elf *elf,
 
         case R_AARCH64_ADR_PREL_PG_HI21_NC:
             overflow_check = false;
+            /* Fallthrough. */
         case R_AARCH64_ADR_PREL_PG_HI21:
             ovf = reloc_insn_imm(RELOC_OP_PAGE, dest, val, 12, 21,
                                  AARCH64_INSN_IMM_ADR);

xen/arch/x86/livepatch.c

@@ -161,16 +161,14 @@ int arch_livepatch_perform_rela(struct livepatch_elf *elf,
                                 const struct livepatch_elf_sec *base,
                                 const struct livepatch_elf_sec *rela)
 {
-    const Elf_RelA *r;
-    unsigned int symndx, i;
-    uint64_t val;
-    uint8_t *dest;
+    unsigned int i;
 
     for ( i = 0; i < (rela->sec->sh_size / rela->sec->sh_entsize); i++ )
     {
-        r = rela->data + i * rela->sec->sh_entsize;
-
-        symndx = ELF64_R_SYM(r->r_info);
+        const Elf_RelA *r = rela->data + i * rela->sec->sh_entsize;
+        unsigned int symndx = ELF64_R_SYM(r->r_info);
+        uint8_t *dest = base->load_addr + r->r_offset;
+        uint64_t val;
 
         if ( symndx > elf->nsym )
         {
@@ -179,7 +177,6 @@ int arch_livepatch_perform_rela(struct livepatch_elf *elf,
             return -EINVAL;
         }
 
-        dest = base->load_addr + r->r_offset;
         val = r->r_addend + elf->sym[symndx].sym->st_value;
 
         switch ( ELF64_R_TYPE(r->r_info) )