From 75d2fa82ec381cb68174bf093e794b0aeee81ca1 Mon Sep 17 00:00:00 2001 From: Ben Pfaff Date: Thu, 14 Feb 2008 08:17:14 +0000 Subject: [PATCH] Explain why a null pointer sentinel must be pushed on the stack. From Valentin I. Spitkovsky . --- doc/userprog.texi | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/doc/userprog.texi b/doc/userprog.texi index 0872f79..5bd0bb2 100644 --- a/doc/userprog.texi +++ b/doc/userprog.texi @@ -1090,10 +1090,11 @@ pointers. Then, push the address of each string plus a null pointer sentinel, on the stack, in right-to-left order. These are the elements of -@code{argv}. The order ensures that @code{argv[0]} is at the lowest -virtual address. Word-aligned accesses are faster than unaligned -accesses, so for best performance round the stack pointer down to a -multiple of 4 before the first push. +@code{argv}. The null pointer sentinel ensures that @code{argv[argc]} +is a null pointer, as required by the C standard. The order ensures +that @code{argv[0]} is at the lowest virtual address. Word-aligned +accesses are faster than unaligned accesses, so for best performance +round the stack pointer down to a multiple of 4 before the first push. Then, push @code{argv} (the address of @code{argv[0]}) and @code{argc}, in that order. Finally, push a fake ``return address'': although the -- 2.30.2