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bug#33174: 27.0.50; Dump fails on GNU/Linux ppc64le

From: Paul Eggert
Subject: bug#33174: 27.0.50; Dump fails on GNU/Linux ppc64le
Date: Mon, 29 Oct 2018 00:22:15 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1

Thomas Fitzsimmons wrote:
Paul Eggert <address@hidden> writes:

Wonderful. Yet another reason we need to get the pdumper branch working. Anyway:

1. Can you use strace and/or GDB to investigate how ./temacs is
disabling address randomization? In the emacs-26 branch, if you run
this command in src:

strace -f -o /tmp/tr ./temacs --batch  --load loadup bootstrap

the output file /tmp/tr should contain something like this:

18406 personality(0xffffffff)           = 0 (PER_LINUX)
18406 personality(PER_LINUX|ADDR_NO_RANDOMIZE) = 0 (PER_LINUX)
18406 personality(0xffffffff)           = 0x40000 (PER_LINUX|ADDR_NO_RANDOMIZE)

I see the above personality calls exactly as you've shown them.

strace never gets to the next execve; the crash happens before the next
execve is run, see below.

18406 execve("./temacs", ["./temacs", "--batch", "--load", "loadup",
"bootstrap"], 0xc521b0 /* 80 vars */) = 0

So there are no more system calls after personality(0xffffffff)? That is, the crash happens immediately before any other system calls? What does 'strace' say about the crash?

For me, the execve is the first syscall after the 'personality(0xffffffff) = 0x40000'. If you're seeing some other syscall there (or are seeing a crash), please investigate why, presumably with GDB.

When I run the command under gdb, it succeeds, so I had to enable core
dumps to get the backtrace:

Core dumps won't help us much I'm afraid. Instead, when debugging ./temacs, please use the GDB command "set disable-randomization off" before issuing the GDB command "run --batch --load loadup bootstrap".

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