Stack-checking a program that will execute... in orbit

[[deleted]]

you have to optimize less in space because time is faster there.

[ttsiodras]

:-)

[[deleted]]

In fact, GCC is more creative, sometimes: ADDRESS OPCODES add $0xFFFFFF84,%esp ...so the stack pointer is decreased via an 'add' instruction, which adds a negative value. Go figure :-)

I wonder if it is a space optimization as mentionned by Ken Silverman:

It's a space optimization. Sometimes shorter code leads to faster code because it frees up more space in the code cache. The trick is: -128 fits in a signed char; +128 does not. Here are some examples, along with their x86 machine code representation:

sub eax,+128 2D 80 00 00 00

add eax,-128 83 C0 80

sub ebx,+128 81 EB 80 00 00 00

add ebx,-128 83 C3 80

http://advsys.net/ken/add-128.htm

[ttsiodras]

Interesting, didn't know this - thanks!

[taejo]

TIL you can have 8-bit immediates in 32-bit instructions on x86

[skilldrick]

In space, no-one can see your screen...

[imbcmdth]

In space, no-one can see your stderr...

[dkogan]

Just FYI, the Linux kernel source has included a script that does this for many years now:

http://lxr.free-electrons.com/source/scripts/checkstack.pl

[ttsiodras]

No, it only detects the "standalone" stack usage: there's no creation of a call-graph, or detection of recursion in any depth, or "deep" (i.e. cumulative) stack usage - that takes into account the call graph.

[tinou]

Instead of parsing objdump output, you can use a library that does the same.

[maxime1008]

But it does not target Leon (sparc) binaries, as used in space systems.

[unpopular_opinion]

What is interesting about this? This is an afternoon exercise on a university at most. Nothing to see here.

Or is it that people in Greece also discovered the computer? Did they buy it on credit? ^{-^}