Hi, I just noticed that a typo is present in the original subject (kvmtool is misspelled.) I assume that some of you filter messages according to their subject, hence this new mail. Sorry for the spam. -------- Forwarded Message -------- Subject: kmvtool: invalid embedded ELF binaries' size Date: Mon, 2 Jan 2017 15:04:50 +0100 To: kvm@xxxxxxxxxxxxxxx Hi, A user of the NoFear project reported a bug ( https://github.com/cappsule/nofear/issues/6 ) suggesting that kvmtool is broken if compiled with a specific gcc version. This issue can be reproduced with gcc version 6.2.1 20161124 (Debian 6.2.1-5), but not with gcc version 6.1.1 20160802 (Debian 6.1.1-11). The function extract_file() writes embedded ELF files to the filesystem: static int extract_file(const char *guestfs_name, const char *filename, const void *data, const void *_size) ... ret = xwrite(fd, data, (size_t)_size); ... } extern char _binary_guest_init_start; extern char _binary_guest_init_size; extern char _binary_guest_pre_init_start; extern char _binary_guest_pre_init_size; I didn't manage to find how _binary_guest_init_size and _binary_guest_pre_init_size are created during the link step, but a quick debug session shows that they're 4 bytes wide: (gdb) disass kvm_setup_guest_init Dump of assembler code for function kvm_setup_guest_init: => 0x00005599b846dc60 <+0>: push rbx 0x00005599b846dc61 <+1>: lea rcx,[rip+0xffffffffffff76a8] # 0x5599b8465310 0x00005599b846dc68 <+8>: lea rdx,[rip+0x22a809] # 0x5599b8698478 0x00005599b846dc6f <+15>: lea rsi,[rip+0x18a2c] # 0x5599b84866a2 0x00005599b846dc76 <+22>: mov rbx,rdi 0x00005599b846dc79 <+25>: call 0x5599b846d9e0 <extract_file> ... (gdb) x/xw 0x5599b8465310 0x5599b8465310: 0x000004c2 (gdb) x/xg 0x5599b8465310 0x5599b8465310: 0x00000012000004c2 Casting _size to size_t in extract_file() is wrong because _size is 4 bytes wide. On x64, xwrite thus fails when the 4 bytes following _binary_guest_init_size/_binary_guest_pre_init_size are different than 0. I think that casting _size to unsigned int should fix this issue, but I would appreciate if someone can explain how _binary_guest_init_size and _binary_guest_pre_init_size are produced by the linker. Thanks -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
