kernel/kexec_file.c: remove unneeded for-loop in kexec_purgatory_setup_sechdrs

To update the entry point there is an extra loop over all section
headers although this can be done in the main loop.  So move it there
and eliminate the extra loop and variable to store the 'entry section
index'.

Also, in the main loop, move the usual case, i.e.  non-bss section, out
of the extra if-block.

Link: http://lkml.kernel.org/r/20180321112751.22196-8-prudo@linux.vnet.ibm.comSigned-off-by: Philipp Rudo <prudo@linux.vnet.ibm.com>
Reviewed-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Acked-by: Dave Young <dyoung@redhat.com>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/kexec_file.c

@@ -792,7 +792,6 @@ static int kexec_purgatory_setup_sechdrs(struct purgatory_info *pi,
 	unsigned char *buf_addr;
 	unsigned char *src;
 	Elf_Shdr *sechdrs;
-	int entry_sidx = -1;
 	int i;
 
 	sechdrs = vzalloc(pi->ehdr->e_shnum * sizeof(Elf_Shdr));
@@ -824,32 +823,11 @@ static int kexec_purgatory_setup_sechdrs(struct purgatory_info *pi,
 						sechdrs[i].sh_offset;
 	}
 
-	/*
-	 * Identify entry point section and make entry relative to section
-	 * start.
-	 */
-	kbuf->image->start = pi->ehdr->e_entry;
-	for (i = 0; i < pi->ehdr->e_shnum; i++) {
-		if (!(sechdrs[i].sh_flags & SHF_ALLOC))
-			continue;
-
-		if (!(sechdrs[i].sh_flags & SHF_EXECINSTR))
-			continue;
-
-		/* Make entry section relative */
-		if (sechdrs[i].sh_addr <= pi->ehdr->e_entry &&
-		    ((sechdrs[i].sh_addr + sechdrs[i].sh_size) >
-		     pi->ehdr->e_entry)) {
-			entry_sidx = i;
-			kbuf->image->start -= sechdrs[i].sh_addr;
-			break;
-		}
-	}
-
 	/* Load SHF_ALLOC sections */
 	buf_addr = kbuf->buffer;
 	load_addr = curr_load_addr = kbuf->mem;
 	bss_addr = load_addr + kbuf->bufsz;
+	kbuf->image->start = pi->ehdr->e_entry;
 
 	for (i = 0; i < pi->ehdr->e_shnum; i++) {
 		unsigned long align;
@@ -858,13 +836,28 @@ static int kexec_purgatory_setup_sechdrs(struct purgatory_info *pi,
 			continue;
 
 		align = sechdrs[i].sh_addralign;
-		if (sechdrs[i].sh_type != SHT_NOBITS) {
+
+		if (sechdrs[i].sh_type == SHT_NOBITS) {
+			bss_addr = ALIGN(bss_addr, align);
+			sechdrs[i].sh_addr = bss_addr;
+			bss_addr += sechdrs[i].sh_size;
+			continue;
+		}
+
 		curr_load_addr = ALIGN(curr_load_addr, align);
 		offset = curr_load_addr - load_addr;
 		/* We already modifed ->sh_offset to keep src addr */
-			src = (char *) sechdrs[i].sh_offset;
+		src = (char *)sechdrs[i].sh_offset;
 		memcpy(buf_addr + offset, src, sechdrs[i].sh_size);
 
+		if (sechdrs[i].sh_flags & SHF_EXECINSTR &&
+		    pi->ehdr->e_entry >= sechdrs[i].sh_addr &&
+		    pi->ehdr->e_entry < (sechdrs[i].sh_addr
+					 + sechdrs[i].sh_size)) {
+			kbuf->image->start -= sechdrs[i].sh_addr;
+			kbuf->image->start += curr_load_addr;
+		}
+
 		/* Store load address and source address of section */
 		sechdrs[i].sh_addr = curr_load_addr;
 
@@ -876,16 +869,7 @@ static int kexec_purgatory_setup_sechdrs(struct purgatory_info *pi,
 
 		/* Advance to the next address */
 		curr_load_addr += sechdrs[i].sh_size;
-		} else {
-			bss_addr = ALIGN(bss_addr, align);
-			sechdrs[i].sh_addr = bss_addr;
-			bss_addr += sechdrs[i].sh_size;
 	}
-	}
-
-	/* Update entry point based on load address of text section */
-	if (entry_sidx >= 0)
-		kbuf->image->start += sechdrs[entry_sidx].sh_addr;
 
 	return 0;
 }