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frame.c: Somewhat explain `FDE'.

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* frame.c: Somewhat explain `FDE'.
        Suggested by Brendan Kehoe

From-SVN: r23243
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Martin v. Löwis 1998-10-23 02:25:09 +00:00 committed by Martin v. Löwis
parent 8d3f83d25c
commit ccb5954fea
2 changed files with 24 additions and 0 deletions
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gcc/ChangeLog
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@ -1,3 +1,8 @@
Fri Oct 23 11:19:06 1998 Martin v. Löwis <loewis@informatik.hu-berlin.de>
* frame.c: Somewhat explain `FDE'.
Suggested by Brendan Kehoe
Fri Oct 23 00:56:11 1998 Jason Merrill <jason@yorick.cygnus.com>
* expr.c (pending_chain): Move up.

19
gcc/frame.c
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@ -71,6 +71,25 @@ typedef unsigned int uaddr __attribute__ ((mode (pointer)));
typedef int saddr __attribute__ ((mode (pointer)));
typedef unsigned char ubyte;
/* Terminology:
CIE - Common Information Element
FDE - Frame Descriptor Element
There is one per function, and it describes where the function code
is located, and what the register lifetimes and stack layout are
within the function.
The data structures are defined in the DWARF specfication, although
not in a very readable way (see LITERATURE).
Every time an exception is thrown, the code needs to locate the FDE
for the current function, and starts to look for exception regions
from that FDE. This works in a two-level search:
a) in a linear search, find the shared image (i.e. DLL) containing
the PC
b) using the FDE table for that shared object, locate the FDE using
binary search (which requires the sorting). */
/* The first few fields of a CIE. The CIE_id field is 0 for a CIE,
to distinguish it from a valid FDE. FDEs are aligned to an addressing
unit boundary, but the fields within are unaligned. */