[avr-libc-dev] [bug #44514] Wrong build option '-mtiny-stack' instead of '-msp8'

[Georg-Johann Lay]

URL:
  <http://savannah.nongnu.org/bugs/?44514>

                 Summary: Wrong build option '-mtiny-stack' instead of '-msp8'
                 Project: AVR C Runtime Library
            Submitted by: gjlayde
            Submitted on: Mi 11 Mär 2015 19:37:20 GMT
                Category: Build Infrastructure
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Build system
                  Status: None
        Percent Complete: 0%
             Assigned to: None
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 1.8.0
           Fixed Release: None

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Details:

Libraries are being built with a wrong option -mtiny-stack:

devtools/gen-avr-lib-tree.sh:49

CFLAGS_TINY_STACK="-mtiny-stack -mcall-prologues -Os"


To query avr-gcc for it's multilib layout, use -print-multi-lib:


$ avr-gcc -print-multi-lib
.;
avr25;@mmcu=avr25
avr3;@mmcu=avr3
avr31;@mmcu=avr31
avr35;@mmcu=avr35
avr4;@mmcu=avr4
avr5;@mmcu=avr5
avr51;@mmcu=avr51
avr6;@mmcu=avr6
avrxmega2;@mmcu=avrxmega2
avrxmega4;@mmcu=avrxmega4
avrxmega5;@mmcu=avrxmega5
avrxmega6;@mmcu=avrxmega6
avrxmega7;@mmcu=avrxmega7
tiny-stack;@msp8
avr25/tiny-stack;@address@hidden


For each line:  Left of ';' stands the multilib subdir, right of ';' are the
option(s) to select that multilib subdir (replace '@' with ' -' to get the
option(s)).

Notice that -mtiny-stack is *not* an avr-gcc multilib option!  The correct
option is -msp8.

In order to query for the multilib subdir for a specific set of command
options, use


$ avr-gcc -print-multi-directory <options>


Example:

$ avr-gcc -print-multilib -mmcu=avr2 -msp8 -Os
tiny-stack


'-Os' is ignored (no multilib option)
'-mmcu=avr2' is the default multilib, hence will yield '.'.
'-msp8' selects the tiny-stack subdir for avr2 and the result is
'./tiny-stack' i.e. 'tiny-stack'.

Also notice that apart from their multilib properties, -msp8 and -mtiny-stack
are working differently:

* -msp8 asserts that the stack pointer (SP) is 8 bits wide *physically*. 
avr-gcc will set -msp8 as needed except for the cases -mmcu=avr2 and
-mmcu=avr25.  These are the only core architectures which intermix devices
with 16-bit wide and 8-bit wide SP.  Or, to put it more precisely:  avr-gcc
uses -msp8 to decomposes these to sets of devices into 4 core architectures.

* -mtiny-stack is an optimization option:  Only the lower 8 bits of SP will be
changed, no matter how SP is layed out physically.  This applies to all
devices and archirectures.





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