linux-kernel - Re: [PATCH] rcu: avoid checking for constant

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Message-ID: <1326365659.2950.3.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC>
Date:	Thu, 12 Jan 2012 11:54:19 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jan Engelhardt <jengelh@...ozas.de>
Cc:	Josh Triplett <josh@...htriplett.org>, paulmck@...ux.vnet.ibm.com,
	laijs@...fujitsu.com, manfred@...orfullife.com,
	dhowells@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rcu: avoid checking for constant

Le jeudi 12 janvier 2012 à 11:34 +0100, Jan Engelhardt a écrit :

> When compiling kernel or module code with -O0, "offset" is no longer
> considered a constant, and therefore always triggers the build error
> that BUILD_BUG_ON is defined to yield.


Why compiling kernel with -O0 is even considered ?

A lot of patches are needed because gcc -O0 is unable to understand some
code is dead code.

  LD      .tmp_vmlinux1
mm/built-in.o: In function `do_swap_page':
memory.c:(.text+0x44dbd): undefined reference to `ksm_does_need_to_copy'
net/built-in.o: In function `ieee80211_tx_status':
(.text+0x221ac1): undefined reference to `ieee80211s_update_metric'
net/built-in.o: In function `sta_info_insert_finish':
sta_info.c:(.text+0x224c62): undefined reference to
`mesh_accept_plinks_update'
net/built-in.o: In function `ieee80211_teardown_sdata':
iface.c:(.text+0x242773): undefined reference to `mesh_rmc_free'
net/built-in.o: In function `ieee80211_iface_work':
iface.c:(.text+0x242cfa): undefined reference to
`ieee80211_mesh_rx_queued_mgmt'
iface.c:(.text+0x242dc2): undefined reference to `ieee80211_mesh_work'
net/built-in.o: In function `ieee80211_setup_sdata':
iface.c:(.text+0x242ffc): undefined reference to
`ieee80211_mesh_init_sdata'
net/built-in.o: In function `ieee80211_if_remove':
(.text+0x243d1a): undefined reference to `mesh_path_flush_by_iface'
net/built-in.o: In function `ieee80211_remove_interfaces':
(.text+0x243df5): undefined reference to `mesh_path_flush_by_iface'
net/built-in.o: In function `ieee80211_rx_h_action':
rx.c:(.text+0x253ba6): undefined reference to `mesh_action_is_path_sel'
net/built-in.o: In function `ieee80211_xmit':
(.text+0x25a254): undefined reference to `mesh_nexthop_resolve'
net/built-in.o: In function `ieee80211_beacon_get_tim':
(.text+0x25c250): undefined reference to `mesh_add_ds_params_ie'
net/built-in.o: In function `ieee80211_beacon_get_tim':
(.text+0x25c28d): undefined reference to `mesh_add_rsn_ie'
net/built-in.o: In function `ieee80211_beacon_get_tim':
(.text+0x25c2a4): undefined reference to `mesh_add_ht_cap_ie'
net/built-in.o: In function `ieee80211_beacon_get_tim':
(.text+0x25c2bb): undefined reference to `mesh_add_ht_info_ie'
net/built-in.o: In function `ieee80211_beacon_get_tim':
(.text+0x25c2d2): undefined reference to `mesh_add_meshid_ie'
net/built-in.o: In function `ieee80211_beacon_get_tim':
(.text+0x25c2e9): undefined reference to `mesh_add_meshconf_ie'
net/built-in.o: In function `ieee80211_beacon_get_tim':
(.text+0x25c300): undefined reference to `mesh_add_vendor_ies'
make: *** [.tmp_vmlinux1] Erreur 1


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