From 218e4395786e51487d27ad432249c27687667b7c Mon Sep 17 00:00:00 2001 From: John Ousterhout <ouster@cs.stanford.edu> Date: Thu, 26 Mar 2020 10:56:00 -0700 Subject: [PATCH] Fix ld output with recent versions of GCC and binutils Recent versions of GCC and binutils produce programs that make use of "Secure COde Partitioning (SCOP)" as indicated by ld's separate-code flag. SCOP adds an additional ELF segment that bears read, but not execute, permissions, and Pintos is unable to load programs laid out in this way. For instance, the version of ld on Fedora 31+ seems to break Pintos' program loading by generating ELFs with the following layout: $ readelf -l halt Elf file type is EXEC (Executable file) Entry point 0x80480cb There are 4 program headers, starting at offset 52 Program Headers: Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align LOAD 0x000000 0x08048000 0x08047000 0x000b4 0x000b4 R 0x1000 LOAD 0x0000c0 0x080480c0 0x080480c0 0x02699 0x02699 R E 0x1000 LOAD 0x00275c 0x0804b75c 0x0804b75c 0x00018 0x00019 RW 0x1000 GNU_STACK 0x000000 0x00000000 0x00000000 0x00000 0x00000 RW 0x10 Section to Segment mapping: Segment Sections... 00 01 .text .rodata .rodata.str1.4 .rodata.str1.1 02 .data .bss 03 The failure follows from Pintos trying to load two segments (00 and 01) at the same address. The failure happens when process.c's load() tries to load the second segment by calling load_segment(), which calls install_page(). Passing noseparate-code to ld reverts to the following ELF layout, and this fixes the problem. Elf file type is EXEC (Executable file) Entry point 0x80480ab There are 3 program headers, starting at offset 52 Program Headers: Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align LOAD 0x000000 0x08048000 0x08048000 0x02739 0x02739 R E 0x1000 LOAD 0x00273c 0x0804b73c 0x0804b73c 0x00018 0x00019 RW 0x1000 GNU_STACK 0x000000 0x00000000 0x00000000 0x00000 0x00000 RW 0x10 Section to Segment mapping: Segment Sections... 00 .text .rodata .rodata.str1.4 .rodata.str1.1 01 .data .bss 02 Signed-off-by: W. Michael Petullo <mike@flyn.org> --- src/Make.config | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/src/Make.config b/src/Make.config index 14219b6..e0afafb 100644 --- a/src/Make.config +++ b/src/Make.config @@ -36,7 +36,7 @@ WARNINGS = -Wall -W -Wstrict-prototypes -Wmissing-prototypes -Wsystem-headers CFLAGS = -g -msoft-float -O -march=i686 CPPFLAGS = -nostdinc -I$(SRCDIR) -I$(SRCDIR)/lib ASFLAGS = -Wa,--gstabs -LDFLAGS = +LDFLAGS = -z noseparate-code DEPS = -MMD -MF $(@:.o=.d) # Turn off -fstack-protector, which we don't support. -- 2.30.2